Locking up at Desktop

Ok my computer ran fine yesterday except it was slow on shutting down but i didnt think anything of it. This morning i goto to boot my computer up it going fine and it gets to the the desktop it freezes i can move my mouse and enter task manager but thats all. And when i try to launch a program thru the Task Manager it locks up when i click on browze (the entire computer)

any help would be nice :-D

 

Start by posting your computers specs?
Include your PSU brand & model

 

Dell
Cpu: 1.8 ghz intell P4
512 Ram
nvidia 5200 256
2 hdd 1 20 gig other 200 gig

 

any one???