The sticky key thing depends entirely upon which key is sticking, and for how long... a ledger holding down the Ctrl key causes really wacky things to happen, but if the key only sticks briefly before releasing again, it can be harder to spot.

The best way to eliminate them from the equation is by replacement - after all, they aren't expensive items.

I work in IT by day, and firmly subscribe to the Sherlock Holmes method... when you've eliminated the possible, consider the impossible! Or summat like that...!

Another thought... are they PS2 or USB? USB keyboards can't be trusted, but USB mice are usually okay.