I've now managed to get the keyboard to respond. After plugging the keyboard into each of the available USB ports (there are 5 on the rear panel and 2 on the front panel) three or four times it finally decided to start working. I've checked the drivers and all are up to date. I'm now thinking that this is a marginal power supply that is having difficulty in holding the 5v rail. Any thoughts?
Iain
USB ports can be very fussy, as they all have their own addresses and record what has been plugged in. Not using safely remove can confuse the issue too.
A very handy little utility that is free and shows you what is or has been plugged in to which USB port and whether it is safe to remove, is USB Deview. You can also use it to remove records that might make the computer think something isn't plugged in when it is. I had terrible trouble with USB dongles in this way on this old laptop I'm using here. As you say though, I'm sure voltage comes into it too: some devices more fussy than others.
You could try a powered USB hub. It has to be cheaper than a new power supply or (perish the thought) motherboard.
If you upgrade to Windows 7 (or dare I say Vista) there is an accessibility button on the login screen. From this you can launch "on screen keyboard" so the original problem would not occur so long as the mouse works.
If you have access to a student (or any child in UK education) you can buy W7 for 43 quid here:
posse - but suggesting a Windows upgrade for a keyboard problem is...well...a tad OTT!
For the OP - unlikely to be a PSU issue. I'm sure you'd see problems elsewhere before this (the 5V rail, and the 3.3V rail usually derived from it) is driving most of the sensitive electronics in there, isn't it?). If there was an issue like that, then I'd be expecting a total crash every time you plugged a device in. It is more likely driver issues. Problem is, as Spamlet says, we put so many USB drivers in our systems, and once unplugged, they just lie there dormant and unnoticed. But then cause issues at the most inconvenient times. I've known keyboards to require several minutes to respond on some 'just booted up' systems. When we moved to hot desking at work, until I'd sat at every desk in the team area, I had very poor startup times with the keyboard. Probably because each docking station had the USB keyboard in a different port.
Alternatively, have you got some strange 'legacy USB' settings in the BIOS that could be tweaked. Though unlikely.
You could just stick Ubuntu on it! :-P ... I'll get me coat.
JW
Probably not related, but worth an FYI, anyway. Last year we had a keyboard problem. When plugged into a PC it would boot normally. However the keybaord would either not respond, or would only send keypresses unpredictably. Occasionally ir would lock the whole dam' PC. Plugging in a different keyboard worked fine. Since this appeared to be a goner (and this is a DIY forum), I took the base off, to have a poke around. Although the keybaord had never had anything spilled on it, the membrane and switch contacts were covered in some sort of slimy substance. Possibly due to the near 100% humidity it had experienced in the preceding months. After cleaning the crud off everywhere and reassembling, it worked as good as new. My conclusion was that this goop was conductive enough to either bridge some of the switch contacts and send continual keypresses, or that it messed up the electronics and got the PC confused.
Oh please. Not for a keyboard!
MBQ
Hey chill out it was just a suggestion.............
Another solution is to remove the login password altogether.
Windows remembers what has been plugged into each port and the drivers etc associated with it. Hence the next time you plug it in, it is recognised and enabled more quickly. It might be that it had managed to cache a corrupt or in appropriate driver for it for some reason, and was hence reloading something that would not work. Going for a port that has never serviced that peripheral before, would force it though the detection and identification process again for that port - allowing an opportunity to correct the error.
Often, there are a couple of USB ports with jumpers to select where their 5V power comes from - either the main 5V rail, or the 5V standy rail (which is is powered all the time so the keyboard remains powered when the PC is powered off, and the keyboard can be used to power it back on). The 5V standby rail has only a low current capacity. It will comfortably feed a keyboard (50mA usually), but if you also have another USB device powered from a USB port on the 5V standby supply, then that may be exceeding the capability of that supply rail.
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