booting problems and noisie pc

i have a home bult pc bout 3 years ago august 2005 and i have

asus p5nd2 deluxe sli mb
2 gig ultra dc memory
2 hds a 250 seagate and a 320 wd just got the wd back from a crash
7800 gtx evga video card
coolmaster 650 psu it replaced an ultra 500 which blew on me literally i could smell burnt electic smell from the ultra when it went
intel pentium d 820 2.8 gig cpu a coolmaster hsf 775 one as big as i could find had to use a mounting bracket under mb for it so big
and a netgear wirless 311 card

ok now the problem is at time the pc will just shutdown on me out of the blue and when i start it up either i got to keep trying to start it from 5-250+ times pressing the on button of the pc it can allso do this when i press the on button it doesnt light up but i can hear the fans still running and if i give it a slight tap on the chassis it can light up and during this whole ordeal even when the pc is on i can get loud rattling noises and high pitch squeels would anyone know what my problem would be i have basic certificate a+ on pc's and i am at a loss and frankly i dont have the money for like compusa tech atm any help would be awsome