The first thing I'd think of is to look at devmgmt.msc in run box (Device Manager)and see if the keyboard is present when you expand the entry and if the entry is present. I've had confirmation from the Vista Device team that once again in Vista, as in Win XP, that Device Manager will not accurately assess "driver health" but it will asses driver presence. The driver device teams have put driver health accuracy off until the next six years. So in other words, device manager can indicate a driver is present, but that doesn't mean it's working. You can get a great example of that in Vista with so many drivers still not working for a gamut of devices. My HP scanner that the Print team said to find a Twain DS driver for that in fact doesn't exist is a great case in point.
Try installing the driver again if you haven't already and my preference is to download the latest appropriate driver from whomever manufactures your keyboard at their site.
You also can try a system restore point to before this happened and if it's awkward to use the tab and direction keys or another keyboard won't work, you can use Startup Repair by following these steps to see if that gets the keyboard back up and running:
What It Can Do:
If you run Win RE's Startup Repair in Vista, it will try to check and repair the following and we're taking about under three minutes usually when it works which is often: (this is not a complete list but a list of major tasks it can perform):
Registry Corruptions
Missing/corrupt driver files (you don't have to guess here--it looks at all of them
Missing/corrupt system files (disabled in Beta 2 as is System File Checker but present newer builds)
Incompatible Driver Installation
Incompatible OS update installations
Startup Repair may offer a dialogue box to use System restore.
How to Use Startup Repair:
***Accessing Windows RE (Repair Environment):***
1) Insert Media into PC (the DVD you burned)
2) ***You will see on the Vista logo setup screen after lang. options in the
lower left corner, a link called "System Recovery Options."***
Screenshot: System Recovery Options (Lower Left Link)
http://blogs.itecn.net/photos/liuhui/images/2014/500x375.aspx
Screenshot: (Click first option "Startup Repair"
http://www.leedesmond.com/images/img_vista02ctp-installSysRecOpt2.bmp
3) Select your OS for repair.
4) Its been my experience that you can see some causes of the crash from
theWin RE feature:
You'll have a choice there of using:
1) Startup Repair
2) System Restore
3) Complete PC Restore
Good luck,
CH