Can you get to the Safe Mode to run your anti-virus software? Can you access the Safe Mode with Networking to download an anti-virus program like Avast or Malwarebytes Anti-Malware from Filehippo.com if you don't have one? If not, see below.
Two thing to try -
Try using the rescue disk from Kaspersky.com. This is a way of getting the computer to boot from this rescue disk instead of the normal method. Go to the site for details.
http://support.kaspersky.com/viruses/rescuedisk
Found this on a forum, see if it helps. This was my next suggestion, trying to access your USB to run an anti-virus program from a Flash Drive.
If you cannot use the Internet or download any required programs to the infected machine, you are going to need access to another computer (family member, friend, library etc) with an Internet connection. Save mbam-setup.exe to a flash (usb, pen, thumb, jump) drive or CD, transfer it to the infected machine, then install and run the program. If you cannot transfer to or install on the infected machine, try running the setup (installation) file directly from the flash drive or CD by double-clicking on mbam-setup.exe so it will install on the hard drive. If you cannot copy files to your usb drive, make sure its not "Write Protected". Some flash drives have a switch on the side which could have accidentally been moved to write protect.
-- Some types of malware will disable Malwarebytes Anti-Malware and other security tools to keep them from running properly. If MBAM will not install, try renaming it first.
Right-click on the mbam-setup.exe file file and rename it to mysetup.exe. If that did not work, rename it explorer.exe.
Double-click on the renamed file to start the installation.
If that still did not work, then try changing the file extension. <- click this link if you do not see the file extension
If using Windows Vista, refer to these instructions.
Right-click on explorer.exe and change the .exe extension to .scr, .com, .pif, or .bat.
Then double-click on explorer.com (or whatever extension you renamed it) to begin installation.
If after installation, MBAM will not run, open the Malwarebytes' Anti-Malware folder in Program Files.
Right-click on mbam.exe and rename it to wuauclt.exe.
Double-click on wuauclt.exe to launch the program.
If that did not work, then change the .exe extension in the same way as noted above.
Double-click on wuauclt.com (or whatever extension you renamed it) to launch the program.
-- Other types of malware may delete the main mbam.exe executable file during installation or when attempting to perform a scan which results in various errors. One way to resolve this is to:
Download and install Malwarebytes Anti-Malware on a non-infected computer.
After installation, open Windows Explorer and navigate to the C:\Program Files\Malwarebytes' Anti-Malware\ folder where mbam.exe is located.
Copy the mbam.exe file to the Desktop and rename it to wuauclt.exe or explorer.exe.
Save the renamed file to a usb flash drive or CD and transfer to the infected computer.
Place it in the C:\Program Files\Malwarebytes' Anti-Malware folder, and then double-click on it to run.
Alternatively, you can download a randomized renamed mbam.exe version (i.e. jdRjuT7Hk.exe) from here and use that.
http://www.bleepingcomputer.com/forums/topic285378.html