Are you infected with klez? If so, download the removal tool and boot to safe mode. Run it there.
If you're just not sure, update your virus scanner, boot to safe mode, and scan there. Make sure that in options, under manual scan, all exclusions are removed. Also, turn off system restore if you are running xp (right click my computer and hit properties, go to system restore tab)
The point... Some bug is likely terminating these processes, booting to safe mode will allow you to operate bug process free.
You can also run spybot in safe mode.
Matt J.
Please always take the time to backup any and all data before performing any actions suggested for ANY problem, regardless of how minor a change it might seem. Also test the backup to make sure it is intact.