when i start my computer it starts fine but all peripherals in usb ports do not work and the monitor does not come on too have tested them in other computers n they are fine what cud be the problem and wat can i do.
It is very likely the power supply or the display adapter. People usually don't think it is the power supply when this happens because the computer turns on and the fans are spinning but there is a good chance you have a bad PSU. Do you have an extra display adapter you can try? If that still fails, try a different power supply.
It does happen once in a while that part of the PSU has died, in particular one of the high amp 12v rails that powers video cards. Lots of them currently come with 1-3 rails or more depending on which PSU you got. Check and see if there is another 6 or 6+2 pin connector and see if it works. But usually, if the motherboard posts and you get the beeps from the BIOS and hear the drive booting, I would start looking elsewhere, like a bad video card or bad DVI/VGA cable. If you are positive those are ok, i would look at the motherboard, because what you are percieving to be your computer starting fine (Since you can't see it, it probably isn't starting fine) is probably not posting. Do you happen to have a motherboard with a post code readout LED?