I've just put together a pentium 1 pc from parts. However, It doesn't start. The psu FAN spins for a second and then stops. I unplugged the hdd and this time the psu fan kept spinning. I PLUGGED the hdd in again and powered the machine up and the fan spun only for a second again with the hdd plugged in. I've tried reseating the ram and the cpu and sprayed ipa into the sockets. I've also tested the psu with a multimeter and all the voltages were fine except the -12v rail which was -10.26v. Any help would be appreciated.

PS. The sellers stated clearly that the components are functional.Power supply should be within +/-5% for all voltages. That -10.26v is outside the +/-5% for 12V which should be ( 11.4V to 12.6V ). I'd try a different power supply.I don't think that rail voltage is relevant to this problem. The -12V Rail was only used on certain ISA and PCI Expansion cards, I've seen it out of spec a lot, probably because it is so seldom actually utilized.

I'd be more inclined to suspect the HDD might have a short.Hi agree with BC about the hard drive. Also make sure the IDE cable is the correct way round red strip NEXT to the power connector drive end and red strip closet pin 1 on the motherboard end. Also have you checked the CMOS battery with your meter that it is around 3.2 volts if less than 3 volts you will need a replacement. What motherboard is it and what graphics card are you using ? Perhaps if you are using an AGP graphics card try either a ISA or PCI card INSTEAD. Also visual check of the motherboard Capacitors is in order. I've already gotten it figured out. There wasn't enough load on the PSU and the ram sticks were in the wrong slots.