The easiest solution is to run your virus scanner and let it remove the virus. Insert the CD or floppy disk with your virus scanner on it. Start the program and follow the directions for locating and removing viruses. After you've purged the virus, try to figure out where you might have gotten it from. You can get them from executable programs, and downloaded files.
Boot viruses can even hide in innocent data-only files.
If a virus does trash your PC's data files or hard disk partitioning, all may not be lost. To keep a healthy computer virus-free, scan ALL software before you install it, whether it's a freeware program from the Net or a boxed program from Puters 'R' Us. Insert each disk and scan it separately. Write-protect original software diskettes so that if a virus does hit your computer, it can't affect the original copy of the program. If you use pre-formatted diskettes, scan at least one of them before using any of them.