Problem with HP computer

I've recently experienced troubles with my Hp Pavilion. I went to the HP site and downloaded the driver updates for several different items. Of course I failed to 1) backup my computer first and 2) downloaded and installed multiple drivers therefore I am not sure which one has caused the problem.

The problems I am having are twofold and the second one may have nothing to do with the drivers at all. 1) I can't use the windows log off or standby/shutdown/restart feature. The switch users does work but not the others. I can logoff through the task manager but I cannot use the task mgr to power down/restart. I can turn off the computer using the shut down on the main log in screen.

xp media center
drivers downloaded
HP quick launch buttons (also deinstalled)
Hp wireless assistance
hp battery check
nVidia nForce chipset driver & Networking controller
AMD Processor Update for Microsoft Windows XP
YUAN EC300 DVB-T Tuner Driver