I have just dust cleaned my machine as the fan was becoming very noisy, now when I try to switch on I get the POST screen then when windows is supposed to load it switches off, the HDD are spinning all fans are working, sometimes I get the start windows last good config screen sometimes not - any suggestions?

My wife is about to kill me as she needs to use it

is it overheating?

if you removed the heatsink you MUST reapply the thermal compound

Agree with jbennett. A lot of the time when you see intermittent periods where the system will be on then just shut off, means the cpu is overheating. Especially, if you hear everything spin up.

Thanks guys forgot all about that

My posting NooB status precedes me

Everything is funky once more and my wife speaks - once again cheers guys

Whewww, that you were gonna have to get a new wife lol

glad you got it solved. Yeah its important, you need to replace the compound if you rattle/remove the heatsink. Dont run your pc too hard for the first month or so when you have applied new stuff - it needs to bed in.