It might be be due to the following issues:
1. Hardware incompatibilities
3. Repair Windows Registry
5. Antivirus programs
6. Bugs in applications
Click Start - Run, type in %temp%
and then click OK.
Once that temp folder is open and you can view its contents, select and delete EVERYTHING that's inside it.
It's all junk and is a good place for "nasties" to hide.
If a few files resist being deleted, that's normal. Leave them alone and delete EVERYTHING else.
Repeat the steps with c:\windows\temp
After you're done with both temp folders, restart the computer.