Unresponsive USB connections (inc. keyboard): Unable to loin

This problem puzzles has been puzzling me for days... please someone help me...

I running a decent/normal spec PC with Vista Ultimate 32bit

I went to start up my computer the other morning, and it booted as normal up
to the user login window. I started to type my password, and realised that it
wasn't typing anything, i thought it a bit stranged but assume the batteries
in my wireless keyboard/mouse had gone so hard wired a keyboard straight to
USB. Still nothing. Restarted a few times. Still nothing. Its strange because
i can see there is power running to the keyboard half way through booting but
by the time it gets to the login window none of the USB ports offer any
activity.

So I press F8 during boot thinking 'safe mode' might work. nope. I'm no
expert so i just run through the diagnostics available in this mode (I can
use my keyboard/mouse while in F8) hoping that it might pick up and be able
to fix any errors to registry. So far i'm having no luck...

I don't know enough to try my luck with 'comand prompt', the last option i'm
concidering is 'Factory image restore' but i'd rather avoid this and am not
even sure if it would fix the problem...

Basically i'd like some advice, i've not been able to find any similar
threads so i assume it will take someone with a bit of knowhow to crack this
one.