You didn't give much info so here is a generic answer. This will cover checking for adware, junkware, viruses and how to get rid of them. If worse comes to worse how to recover your files and reset the the puter back to factory settings.
This program gets rid of most adware and browser hijackers.
http://www.bleepingcomputer.com/download/adwcleaner/
This program gets rid of most of the junkware. If you use this program, be careful if you have a toolbar that you want to keep.
http://www.bleepingcomputer.com/download/junkware-removal-tool/
If they do not remove it then scan for viruses. It is important to run both ESET and Malwarebytes, what one might miss the other will catch.
First try Malwarebytes in safe mode. Make a bookmark of the link below or make a shortcut to it on your desktop.
http://www.malwarebytes.org/products/
The link below show how to start Windows in Safe Mode or Safe Mode with Networking.
http://kb.eset.com/esetkb/index?page=content&id=SOLN2268
When it boots to the desktop then click the the bookmark or shortcut you made. Download and install the free version and do a complete deep scan of your system. If it finds anything and it can not stop and delete it you will need RKIll to kill it.
If Malwarebytes does not find anything then try ESET online scanner to check for a virus. The first link is the online scanner. You need to USE IE while in the safe mode with networking to run it. The second link explains it.
http://www.eset.com/us/online-scanner-popup/
http://kb.eset.com/esetkb/index?page=content&id=SOLN2921
Some viruses can be found but not stopped to be deleted. RKill can find and stop the viruses that others can not. Once the viruses has been shut down the security program can then deleted it. The first link below discusses how it works and it is VERY IMPORTANT to read this page. The second link is for the virus removal guides offered by Bleepingcomputer. You will need another puter to download RKill and malwarebytes. You will need both of them on a thumb drive, DVD or a CD. RKill has different filenames because some malware will not allow processes to run unless they have a certain filename. Therefore when attempting to run RKill, if a malware terminates it, try a different filename. READ the instruction carefully on how to use the programs together.
http://www.bleepingcomputer.com/forums/topic308364.html
http://www.bleepingcomputer.com/virus-removal/
Download links for RKill.
http://www.bleepingcomputer.com/download/rkill/
If you can not boot into Windows to make a backup of your files then you can go to the link below and read on how to boot the system from a thumb drive to recover what you want. If you have a Windows 8 or above then you need to turn off secure boot and select boot from USB before using the thumb drive. The thumb drive boot will also allow you to check out the rest of the puter. It helps to have a thumb drive or a external drive to copy your data and files to. The link below also has a list of Linux live and other programs that can help you solve this problem. Read the article completely, there can be problems using these if you do not know what you are doing. I make no guarantees.
http://www.pendrivelinux.com/
You can also download a Live Linux CD ISO to boot the lappy if it has a CD/DVD. I use this one. You can also use the above thumb drive boot option to boot up Linux Mint.
linuxmint.com
Once you have recovered what you need you can reload your OS.
Since you did not list the make, model and OS this part is a generic answer. Some or all of it might help you.
Make sure you back up all your files before doing this.
If your resetting a lappy, make sure you have the AC adapter plugged up. You do not want this process interrupted. This should take one or two hours. It is best to check on it to make sure everything is going fine.
It is best not to boot into Windows to start this process.
If you can not boot into Windows then try Advanced boot options. When you press the power button, start tapping the F8 key. You will see the advance boot menu. Select repair your computer. (This option is available only if the tools are installed on your computer's hard disk.) Select your language and then enter your user name and password. Then click on (brand name) factory Image Restore and next. Answer the question and it should start the recovery back to factory settings.
Recovery from the recovery partition
When you press the power button start tapping the F key for your puter and the BIOS menu will open. Select recovery from the menu, answer the question and the recovery should begin. Depending on your puter this will take one to two hours.
Manufacturers BIOS menu F key
HP/Compaq ESC
ASUS Del
Sony F2
Samsung F4
Gateway, eMachines F10
Acer, Dell, Fijitsu, Gigabyte, Toshiba F12
Your BIOS menu should look something like this. Yours might be different. I am posting this to give you an idea of what it looks like.
ESC = BIOS menu
F1 = System Info
F2 = System Diagnostic
F9 = Boot Device options
F10 = BIOS Setup
F11 = System recovery