Its not uncommon that your computer gets infected with viruses and doesnt boot in windows normally. So here is a solution to the problem, which should help.
1. Shut down your computer from whatever state (Stuck, blacked screen) it is in.
2. Hit the restart button and wait for the Screen to come to life with the Bios.
3. Just as the computer passes Bios, press the F8 button repeatedly till the time you get the custom boot menu for windows. Select “Safe Mode” from the menu and let the computer proceed to Boot in safe mode.
4. Now assuming that your computer has booted successfully in safe mode, its time that you install a good anti virus. Although there are many options available for an antivirus. However, based on user ratings over the internet, the best antivirus for 2012 is Bit defender 2012.
5. Simply go to the website of Bit defender and download antivirus from the downloads page.
6. Install the antivirus in Self Protection mode and let the anti virus install properly.
7. Once done, Run a full system scan and the anti virus will find all the malignant viruses and files in the computer. Once the scan is finished, disinfect all the files and let the process complete.
8. Restart the computer in normal mode now and you should have all the viruses disinfected. You will notice that your computer will also have improved performance depending on the virus that your computer was infected with.
So for all the virus stricken users, try it out and let us know in comments how it worked out for you. Stay tuned!