Computer turns then turns off really fast HELP PLEASE!!!!

[Souporsalad]

Hello i recently sold my friend a computer i build about a year ago and it was working perfectly fine fresh windows 7 new ram and a new hd and then when i gave it to him it was working fine for about a day then it started to turn off after 5-15 minutes for about 2 days and now it wont even boot the fans wont even make a full rotation before it turns on and i checked all connections and everything.
Specs
Asus m4n75td-mobo
patriot pc3-10600 1333MHz ram 2g x 2
AMD athlon II X4 2.8 GHZ
ati raedon 5570 1gb
seagate 250 gb serial ata HD
EXTREME 450 watts atx PSU

 

[blink180heights]

The did you use the Stand off screws which go under the mother board to separate the case from touching the mother board? then screw in the regular screws to secure the mother board? i was a noob and this happened to me, i didn't put the stand off screws under the board. This might help you because if you don't do that, it will short circuit your power connection to the board.