I have recently begun to have a problem on power up. Once the PC has been running during the day, all is fine, but the problem happens after it has been switched off for a few hours (mostly overnight). On first power up the machine dies after a second or so, before the beep (which I presume comes at the end of the POST). It will then not switch on at all. However, if I disconnect the mains lead at the back, wait a few seconds, plug it in again and then retry, the machine boots up perfectly.

Is this likely to be a power supply issue (currently running a 400w power supply), or something more serious on the mainboard? Am I correct in assuming it is hardware rather than software related?

I’m running an Athlon XP2600 with Win XP SP2. Plenty of hard disk space. 1Gb of Ram (recently upgraded from 512, but the Ram isn’t the problem – the symptoms are exactly the same if I remove the new Ram, and the system is recognising and using whichever amount of memory I have on board).

hello dunthorne and welcome to pchf

unfortunatly it is not my area of expertise but it sounds like it could be a power supply problem

one of the tech team will be online shortly and be of further assistance to you

genie3251

Does sound like a hardware problem. Could be power supply or motherboard, however it could also be a sticky switch on the front of the case. Depending on how you BIOS is setup in Power Managment (Instant Off or delay), if the button is stuck in, then it will switch off after the first couple of seconds.

Thanks for the advice. I'm pretty certain it was the PSU. I took a working PSU out of an old machine I'm keeping for spares, connected it to just the mainboard (including graphics card), fan, hard drive and wireless adapter, and the machine booted up with no problem. I then reconnected the old PSU to check, and the problem re-appeared - so pretty clear evidence.

I'll get a new PSU, but how big a PSU do I need? The faulty one was 400w, and the new one I'm using temporarily is only 300w, so is not going to be sufficient (so I've not reconnected all my optical drives etc to save power). When all is reconnected, the spec. will be:
Gigagbyte KT400 mainboard
Athlon XP2600 CPU
1 Gb Ram (2 x 512)
Maxtor 80Gb hard drive
Hercules prophet 9600 series 128Mb AGP graphics card
CD-RW
DVD-RW
floppy
internal Zip drive
USB optical mouse
USB wireless .11g adapter
All other USB devices have their own power supply (scanner, printer)

Thanks for the help

hey dunthorne,

i would go for 400-450 watts that should be enough and also i wouldn't buy a cheap one either

genie3251

This is a good site you can use to work out how much PSU you need.

What Power Supply Do I Need - eXtreme Power Supply Calculator