Chaltab.
I suggest you scan you computer with some fancy virus checking software. may i suggest http://housecall.trendmicro.com/ and http://www.pandasoftware.com/products/activescan/com/activescan_principal.htm. And it would also be prudent to check for spyware
http://www.safer-networking.org/en/index.html.
then, since your running xp, its in your best interest to have a virus program installed as well as a firewall (even if its just the windows firewall) Take the time to configure it as its worth it.
hmmm, now that i gave all that info i realize i should have asked a few other questions.
1) have you rebooted? and if so does this problem still occur?
2) are you having other issues? (ie, whats the reason you initially tried to open the taskmanager)
I would then ask if anything out of place is running, but kinda hard to check if you cant run task manager
-Darth Simon