OK, due to the fact your anti-virus security program is detecting a virus and then that virus is programmed to turn off your anti-virus application so it is unable to remove it, (which is a common practice of more sofisticated malware these days) I do believe you have a virus, and this is not an over heating issue as one poster wrote about. If your anti-virus application were not notifying you of an infection and then being shut off, I would agree an overheating issue was more probable, but that is not the case here.
Now, the individual who posted the steps to running a seperate anti-virus off of a bootable CD has it correct. That is one method of attempting to clean up a system which is shutting down security software installed on a system. However, if you are not highly experienced in these tasks, you could do something wrong, or miss an important step in ensuring your computer is disinfected.
The reason a seperate anti-virus program run off of a CD is possible, considering the fact two anti-virus software applications should never be on the same system due to how this causes huge conflicts which can result in both having an inability to properly perform their tasks, system instability and even system crashes, is because running a program off of a CD is not installing it on the system. So, as long as you actually run it off of the CD/DVD and do not actually install onto the system you could clean up the infection. However, this takes some skill level you may not possess. There isn't anything wrong with being less experienced with computer systems, but we do need to be honest with ourselves when evaluating our skill levels and not be embarressed in getting help when we need it.
If you do not have the skill level needed to run a anti-virus application off of a bootable CD/DVD, I strongly encourage you to seak out additional help from those who have the experience. You have two basic choices on where to receive this assistance, from a reputable repair shop in your area, or one of the many online anti-malware forums dedicated to assisting others in the removal of infections.
Now, I highly reccomend forums such as HighjackThis, or those who use that utility and a few others and direct those who log onto the forum on how to use the tools step by step. These people are highly experienced and have vollunteered their time and efforts to aid the internet community in combating the malware creators. However, please keep in mind that all of these forums take a bit of time and effort on your part to clean up your system as they all walk you through the steps you need to perform. You will be required to sign up at one of these many forums, then follow the instructions on how to download certain tools such as HighjackThis and others, how to properly install and then run scans with the tools. After you run the scans you will need to learn how to save the scans into reports and then upload those reports to the forum, where the experts review them and then provide instructions on what to remove and how to do this. You can see that it can take a bit of patience and time when you go this route, but it is free and there is the factor of learning new skills. It really isn't difficult, just time and step intense.
If you do not have the time, are worried you are not skilled enough to perform these steps even with instructions, then your next choice is a local reputable repair shop. You can take your system into a shop and a technician will check out the situation and do everything needed to clean the system up getting rid of all malware, and then return it to you in good condition. However, this will cost you some money, so be prepared for that eventuality. None of these shops work for free of course, unlike the many vollunteers at the anti-malware forums in the usenet community.
If you wish to go the route of an online community, simply type HijackThis into any search engine, Google is good, and you will find many different links to forums devoted to this task. Visit several and check out the forum. Read posts, and also read the sticky notes at the top of the forum topics and it is usual practice for initial steps in what utilities to download and how to install and generate reports, with additional instructions on how to upload those posts to the forum will get you off to a good start. Once you upload your first report an expert will review it and then post in return with the next steps you need to complete in the process.
There is one forum I am aware of which has the added component and benifit of a chat area where you can allow the expert to actually remotely log onto your system and do most of these steps for you. It is a lot quicker, but you would need to feel comfortable with them and have a certain level of trust that they are who they say they are. They are, but don't take my word for it, browse to the website, read the different posts where others are receiving assistance, and become familiar with the experts and how they work. I can assure you this is a good group and they are dedicated to helping out the internet community and combating malware writters. Here is a link you can click so you can browse the site and see if it is something which may be of value to you.
http://groups.msn.com/FreewareandShareware/welcome.msnw
The forum is at MSN, so you will need a passport to log on, but if you have a hotmail or windows live email account then that is your passport. If you do not have one of these resources the logon screen will offer the ability to abtain a passport. The passport is free and is all of the communities.
Now, all of the tools you will be using to clean up your system are free or shareware. Which is how this group initially got started, as a freeware and shareware group that tested such software products and provided reports on how good these are, and whether or not the contain malware or are malware or spyware programs, or if they tend to download malware without your consent when you atttempt to install the program. You can browse the different areas of the website by clicking on the links at the left of the page. You will see the message boards, links to the freeware and shareware programs they reccomend for use, etc. Once you become familiar with the group you then need to sign up as a member, which is free too.
I know all of this sounds intense, but if you take it a step at a time it is not that overwhelming. Really. I highly reccomend many HijackThis forums and the Freeware and Shareware community specifically. If you go the route of Freeware and Shareware you will also have to join their chatroom if you want an expert to fix the issue for you.
Good luck and I hope you get your system cleaned up right away. Who knows what your infection may be doing inside your system. Is it simply benign, or is it stealing your personal information and "phoning home" with that information to the malware creator? These days malware writers do so for the gain, not for the fame and longer as they once did.