It was a working pc for the last 2 years.(new). I made a alteration in its bios(uefi). Then pc cannot boot. No POST. NO BEEP. BUT CPU FAN WORKS AND STOPS REPEATEDLY. Then I erase cmos battery and even replace the cmos battery. Now the cpu fan works well continuously. But no Boot & POST. NO BEEP. Without ram there is a beep. keyboard and pendrive flashes once. But no beep and boot. I checked with two RAM STICKS. Still problem. Ram may not be a problem. then WHAT? If hdd is the problem, then we can get a display of saying hard disk error. So it may not be the problem. I am using a pendrive os also so that it may boot from pendrive os. But no booting.... THANKS IN ADVANCE.....