sata hard disc sometimes undetected

[kenlitting]

i have a dual core desktop with 160 gb sata hard drive and asus P5GC-VM/S MOTHERBOARD & 1 GB DDR2 RAM LOADED WITH VISTA ULTIMATE sometimes when i start my pc it shows bios and then shows reboot and enter device i found that my hard disc is not detected so i opened up system checked sata cable to hard disc drive all is fine then i restarted all is fine working . could someone tell what s the fault . no sata cable is loose actually its a brand new one

 

[Hughv]

Could be a power supply problem.