My old file server died so I ordered new parts yesterday to build a replacement. The new parts:

Motherboard: ASUS M3A78-EM
CPU: AMD 4850e
RAM: OCZ 2*1GB DDR2 800
Graphics: None (integrated)
Case: In-Win MicroATX
PSU: 400W (included with case)

I've kept the hard drive and DVD-RW from the old machine.

So, I've built it and when the moment came to first turn it on there was disappointment. For the first power up I had a SATA hard drive connected and the DVD-RW on the master primary IDE channel. Firstly, the system doesn't power up unless you hold the power button for an amount of time (can be anything from 1 second to 4 seconds). When it came on the disc access light was flashing slowly and consistently on the front of the case and the access light on the DVD-RW was flashing. There was no media in the drive. Secondly (and a lot more importantly) there is no graphics output. I've tried both the VGA and DVI outputs on the board but got nothing from either. Since I can't see what's going on I don't know what's happening (whether it's attempting to post or not) but there are no sounds at all (no beep codes). I thought the reason the system was attempting to access the DVD was becuase it was looking for something to boot from, so I disconnected the DVD-RW and left just the SATA drive connected. This time there was no flashing light but no signal to the monitor still. I've tried connecting an empty hard drive to the master on primary IDE but this doesn't help (there's no flashing light but no signal to the monitor).

The problem with the power button along with the fact that the PSU came with a cheap case is making me think it's the PSU that's at fault. I'm gonna try and swap my old PSU in but I don't know if it has the correct power connector (20pin + 4 pin). Does anyone have any ideas? As the title says I'm slowly going insane with hardware...

Erm. I forgot to plug in the motherboard power connector.

:shhh:

More haste less speed...it's true you know!

it took you 3 and a half hours to figure that out

well, it did take me about an hour to figure out that i had put the switch in the wrong place :P

Reminds me breaking into sweat as I tried to boot a friend´s pc for the first time after building it from sketch. Forgot to put the RAM into it .

Just a few minutes to have figured it out..

Building a mate's PC about a year ago and it wouldn't turn on.

Eventually found that although it looks the same, a floppy-drive power connector is NOT a 4-pin fan header... :dunce:

having the ide cable connected the wrong way will make the drive give a flashing light error. good news is it's easy fixed. take the ide cable out, rotate it 180° and insert.
small tip. the red wire on the ide ribbon cable indicates pin #1. this goes closest to the power input.
newer ide cables will not let you connect it the wrong way. older ones unfortunatly do. same as older drives.
the small molex is not needed unless you play music cd's directly from your drive. this lets you completely bypass sending the music through you cpu and ram and plays from the drive straight to the sound card. that's why some drives have a play/pause and a skip (forward) button. bus mastering used to be important (very low end systems) but can still be used today.
i hope i'm not too late. ditch that cpu and for a similar price get this http://www.ebuyer.com/product/135663 more cache which is important for lfs. and a much better chip all round. if you could stretch the cash a tad more, you could up it to the 5600 or even a 7750 (@ £64)

Quote from dadge :

having the ide cable connected the wrong way will make the drive give a flashing light error. good news is it's easy fixed. take the ide cable out, rotate it 180° and insert.
small tip. the red wire on the ide ribbon cable indicates pin #1. this goes closest to the power input.
newer ide cables will not let you connect it the wrong way. older ones unfortunatly do. same as older drives.

I didn't think you could connect them upside down due shape of the connector and recess on the device (see attached image).

aye, and some drives have the "nick" on the top and bottom of the female connector. that's a newer ide cable. it will have the nick on it to prevent incorrect connection. think of it as a FYI for times when your looking at older machines.
you wouldn't believe how many "builders" get this bit wrong. i can't believe it took you longer than 30 mins to realise that no beep=no power to the mobo. but hey it's sorted now so rock on!!!!