System hangs after resuming from standby

Previously my pc used to go in standby mode n then all fans, cpu fan, lights etc wud turn off. But its not happening now. It just enters stand by mode and when i try to wake it up, there is no response and i have to reset the whole pc.

Intel 541
asus p5gpl
2gb ddr1
160 n 250 sata
8600gt

i tried whatever i can to correct the problem bt no luck.

What os are you using? If you are still on vista, install sp 2. I had this bug. It used to go to standby and never wake up