Windows Vista Vista freeze up after boot

[Spudley]

Hi,I turn on my pc eventually get to desktop screen(has slowed considerably since start of problem last week).After a couple of minutes vista freezes,i can still use mouse pointer but my cpu dualcore usage meter freeze's and my hardrive seems to stop running aswell.I left computer on for a hour,gone back to it and its still frozen.
Ive had computer nearly 18 months and its been great
My computer:

core2duo e6600 2.4ghz
2gb ddr2 667mhz
500gb hardrive
Asus p5 650i

Any suggestions,ideas would be much appreciated.

 

[kemical]

Do you have a cleaning regime? Anti-virus/spyware and the like? If not try AVG and Adaware (can be found through google). Also this utility :

Download CCleaner 2.11.636 - FileHippo.com

is great for cleaning out old files and tidying up the registry..