Odd keyboard issue...

[#1]

Strange things happening with my keyboard:
Not sure how best to describe this but I can no longer press the same key twice in succession whether it be letter, number, backspace/delete or cursor control.
The keyboard is quite old (probably older than 6 years) but has been fine up to a week or so ago. I have replaced batteries (twice), checked for latest drivers and checked settings all to no avail.
It's most likely on the way out but thought I ask here to see if anyone has any other ideas of what to check for. As it is a Russian keyboard, too, I don't really want to be without it.
(Tried to type this using words without double letters but that is almost impossible to do - spellcheck has helped ;))

[#2]

Is it a mechanical or electrical type keyboard? If the latter try taking it apart and cleaning the membrane between the keys and the pcb below. If the former some IPA may be necessary (Isopropanol rather than beer!)

[#3]

It's mechanical.
If I turn it upside down and shake it sounds like something metallic moving around.

[#4]

You could also try an air duster on it. Or a strip down and see what is loose.

[#5]

Quote from: Hairy

Or a strip down and see what is loose.

Ok - so now I'm naked and still can't work out the issue
SWMBO has lent me her wireless keyboard and the same issue appears so it seems it's got to be a software problem.
A reboot was performed only a couple of hours ago so don't think that is necessary.

[#6]

OK - some further researrch and I came across someone else with a similar issue. It was resolved by switching off Filter Keys within Make the keyboard easie to user within Ease of Access Centre.
Whether that has always been on and something has interfrered with it's use or a recent Windows update turned it on I have no idea. Anyway, problems solved

[#7]

Quote from: Mav

Anyway, problems solved

apart from......

Quote

If I turn it upside down and shake it sounds like something metallic moving around.

[#8]

@Mav  You don't happen to have a cat do you? 
The number of times mine has caused similar problems are legion   and as a result she's had so many 'flying lessons' that she should soon get a full Pilot license.
M..

[#9]

Quote from: Mav

OK - some further researrch and I came across someone else with a similar issue. It was resolved by switching off Filter Keys within Make the keyboard easie to user within Ease of Access Centre. Whether that has always been on and something has interfrered with it's use or a recent Windows update turned it on I have no idea. Anyway, problems solved

Its one of those things Windows will turn on for you if you hold down the shift key "for too long" or rapidly tap it.

[#10]

@shutter I think what I am hearing may just be some silver foil or something similar. Doesn't seem to be having an adverse effect on usability
@MauriceC No cat or any other pet - could it have been a mouse? Apparently they've been eating the soap in the bathroom so who knows
@avatastic  It seems 5 rapid presses of the shift opens a box asking if you want to go to the Ease of Access Centre. If I click the link I can see Sticky Keys is off although the option below to turn Sticky Keys on when Shift is pressed 5 times is on. I have turned this off now although Sticky Keys being on doesn't give the issue I had yesterday. That still seems to be a result of Filter Keys but can't see yet how that could have been accidentally turned on.