Weird task manager occurence.

I posted because I have this niggling occurence in task manager that happens only on my main gaming computer but doesnt on all my others.

After booting, the instant after the Windows XP (light blue) welcome screen disappears, when I turn on the task manager, it shows the running processes etc. but DOES NOT show the user names for the processes. SYSTEM is there sometimes but not MY actual username. My other gaming computer has the names up straight away. The usernames do eventually appear but only after my user ID becomes active, shown by the "users" tab in task manager (only if fast user switching is on.)

Basically, after a clean format and reinstall why does task manager show this behaviour. All my other computers have the user ID active the instant the welcome screen goes away, just not mine.

There are no other problems with the computer, only the slow user ID. Could this be a hardware problem, or even a virus or Ad-ware even though the computer is not even connected to the internet but on a seperate home network?

Any help would be much appreciated.