kaled - 1:17 pm on Dec 12, 2009 (gmt 0) 1) You should backup your work (and verify the backup). Kaled.
It sounds like your system is badly compromised - what security software is installed?
2) Your copy of Windows may be genuine, but perhaps you are running something else which is not. You should try to identify the rogue program (starting with a full virus scan).
3) Others may recognise the symptoms you have described and may be able to offer a simple solution, however, I recommend a clean install of Windows from CD (not a repair install). Then, keep the system as clean as possible with no unnecessary software.
4) Consider partitioning your hard disk and installing another copy of Windows. That way, you should always have a working system.
1) You should backup your work (and verify the backup).