|May be powersupply, may be faulty motherboard, could be a faulty device attached to motherboard such as floppy, optic or hard drive, or AGP/PCIe /PCI card.|
Start by stripping down to barebones. ie: Disconnect all drives and take out all cards except 1 stick of ram, Graphics. Leave only CPU with fan, keyboard & graphics.
Try booting up into BIOS setup. If the bootup is still sporadic then you have narrowed the field to powersupply & motherboard. When you post back after doing some testing, please include detailed description of the system including make/model numbers.
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