Hello again, No I do not believe it is a virus and it has something to do with the startup procedure in Windows XP. Since you can not access Safe Mode or anyother mode I will say that you cannot access into windows either. If that is correct then the only thing that might work with out having to reinstall Windows and all of your apps is to do a repair of windows. For this you will need access to another computer that works and has a CD-R burner or DVD burnaer on it. The link that I am going to give you I would suggest printing it out and reading it very carefully and also follow the instructions to the letter. Oh one thing when you use Nero version 6 to make the resulting CD the image file you are going to use will have a img file extension on it for use with Nero it has to be changed to ima.
Build an XP-SP2 Recovery Disc = http://www.pcmag.com/article2/0,1759,1747010,00.asp
After the disk is made the next site will explain itself as to doing a Repair
How to Perform a Windows XP Repair Install = http://www.michaelstevenstech.com/XPrepairinstall.htm
I hope this is of some help and it is the only way I see of doing this with out reinstalling everything
One other thing I would suggest making a backup of all of your data from this hard drive, since you cannot access this drive thru Windows on your system I would suggest taking the drive into another computer and setting it up as a second hard drive and then using a file transfer program like Windows Explorer or Total Commander to manually backup your data.
If you decide to go this route and you think you do not have the skills to accomplish these tasks please get someone to help you with these tasks.