Need help , pc freezes

Hey, ive got a

AMD 3500+ , Nvidia 6600GT , Audigy 2 zs soundcard , and a A8N-SLi
Deluxe asus motherboard ,with a 380w antec power suply.

It all worked fine untill yesterday , normally my pc is on for day and
night , but when i got out of my bed yesterday and wanted to take a
look at my emails , my screen didnt react anymore. so i had to reboot
but then it suddenly freezes at the bios startup screen (not windows).
but sometimes my pc wont even show anything... I didnt install
anything special and ive got the pc for a year and a half now.
Friends told me that it might be something with the power
supply,motherboard , cpu or gfx card...
I had the same problem a few days ago , came back from school ,
watched my pc but was freezed in windows , took the power supply
cable out for a few hours and reboot , then it worked...Now ive
almost tried everything , removed my gfx card , ram , soundcard , and
sometimes i get a long beep when i try to start it up then. Any help
would be very welcome cuz i realy need the computer asap.
please...