Okay I left my computer on pretty long last night, I have an Antec 900 case though so it shouldn't be problem (I hoped)

This morning i go to turn on my computer and the lights and fans turn on for a second and then it powers down. Nothing comes on. I click the power button again and nothing happens. If I turn off the power supply via the switch in the back for a few minutes, and then turn it back on and pus hthe power button, same thing, the lights will flash but thats it.

This is a recently bought case, not even a year old yet,
4gb ram,
AMD phenom 9600, Gigabyte mobo (dont know exact)
and a 750 watt PC and Power PSU

anybody have any ideas why?
it did this about a week ago and we worked on it for a few days and all of a sudden it started working for no reason. leads me to believe maybe something in the PSU is overheating or something?

Most likely the PSU, bad memory or bad board.

Bad memory you should be able to test by swapping them around and single sticking it, but I doubt this is it.

Bad power supply is most easily tested by bringing your case into a shop that can test it for you. You might see if they have a bench power supply they can hook it up to as well as a power supply tested since the larger power supplies are somtimes harder to troubleshoot since they occasionally fail only under heavy load. In order to do this (if they don't understand what you are asking) just hook up MB, video and primary HD and see if it still won't power on.

i hope that power supply is sort by power or some thing,so first you must cheque the power supply, if not ,after you can do the any other way,so please tell about your power supply?????