b n m , keys not working after reboot

[#1]

My mother's PC has a Microsoft Curved Keyboard 2000.
Frequently after a reboot the b n m , (comma) keys fail to work for her. Not good when the first letter of her password is M!.
So far turning NUMLOCK off/On several times has solved it temporarily. I have now uninstalled the current driver and rebooted and all seems fine but will keep an eye on it for her. But has anyone come across this before?
Web searches tend to suggest it's a battery issue but this is a wired mouse.

[#2]

Turn it upside down and give it a quick blast with compressed air - it could just but dust/dirt under the keyboard.
It could also be a failing keyboard membrane or the battery issue you mentioned.
Don't do what I did with my laptop and give it a quick hoover with a Dyson - it took me half the afternoon to get the key caps out of the hoover and back onto the laptop !

[#3]

Definitely can't be a battery issue.
Will give the compressed air a go but am not convinced that could be the issue as 1) the keyboard isn't that old and 2) if it was dirt/dust would it really start working again simply after pressing the NUMLOCK key a few times? Of course, the NUMLOCK key could be a red herring

[#4]

Double check for malware etc and run TSSDKiller to check for rootkits just to be on the safe side.
Also plug in a seperate USB keyboard at the same time - see if the problem happens and if it does if it happens on both keyboards. This will rule out either the keyboard or may help pinpoint it to a driver or something else misbehaving.

[#5]

Full bill of health with all scans.
Unfortunately I don't have a spare keyboard here so may have to bring one next time.
Will do a few reboots over the evening and see if the issue returns since I removed the previously installed driver.

[#6]

This may help!

[#7]

Thanks, for the link.
If the problem doesn't appear to be resolved over the next few hours of reboots then I think I will simply give my mother one of my old, but unused, keyboards.

[#8]

If you borrowed your mother's keyboard and experienced the same problem you would be pretty darn sure it is a hardware issue.

[#9]

Sensible suggestion there RR, that is precisely the technique I used to sort out whether an issue was keyboard or computer, but a word of caution, sometimes when the cause of a problem is an electronic issue, the slightly different  voltages on a different PC can hide a problem!

[#10]

I'll try RR's suggestion as we're going home for a couple of days.

[#11]

SWMBO brought one of our old (around 7 years) but unused keyboards to my mother's to try. Worked, no problems whatsoever.
We've left that with my mother and decided to simply discard the other one. Also noted that the '&' frequently failed to work yet the 7 always did - don't understand this as it's the same key and, if it was a problem with either or both Shift keys, then surely all upper case characters would be affected
Anyway, all works now so alls well and all that

[#12]

Sounds that the chip that does the encoding was on the way, or an electrolytic capacitor had gone u/s and the chip wasn't getting the correct voltages. Glad it's sorted anyway.