You first need to see if it still has a belt that is on both pulleys. If belt is there, push down on the sliding handle to see if the belt gets tighter. Now find the cable clamp near the top of the handle and identify the drive cable. Loosen the clamp and pull the drive cable housing down about a half inch toward the engine. Tighten clamp and try the drive. You should only have about a half inch of free play on the sliding handle. If the mower tries to go without you pushing on the handle, you tightened it too much - back off on the adjustment. Ideally the wheels will not turn if you pick up the back end with the engine running and handle returned to the top of it's travel. However, sometimes the 'right' adjustment will turn the rear wheels very slightly/slowly, not enough to move the mower.
There are several other things that might be wrong with the drive, so get back after doing this check/adjustment which is routine maintenance.

Yes, belt is on, cable not snapped. There was a black plastic clamp thing holding the cable and I surmised it was loose...tightened it up...saw the cable slip as I pushed the handle...tightened more and the plastic piece crumbled into pieces! Well, after 14 or so years I guess I can't complain...wish it were made of metal! The dealer was closed. I am hoping its just the little plastic part. I clamped a bent washer over the cable and tightened and it seemed to work.

Questions:

I have never changed the belt, should I do so? How about the cable?

The cable would not stretch over time, right? To get that half inch play it seams I am almost at the end of the cable...just to where ..the outer metal covering ends....ie you have the actual thin cable...covered in the metal house for about 4 " near the handle then covered in black plastic the rest of the way down.

Its a toro model20043 SR21S.

Yes, there's some cable stretch but most of the adjustment is used up by belt and pulley wear. The bare steel cable housing section is left that way for adjustment purposes. Do not replace the belt unless you have to. They can outlast the mower. You could have several seasons left on it. You won't really know until you get the right clamp on it and see what you have. You can probably get away with much more free play on the handle too. You just want it to go as fast as you walk when cutting and to not drive at all when you're pulling back. This requires a short 'coast' at the end of a run if you need to pull back, but if the free play is insufficient it will keep driving, making it difficult to manuever. So more free play will give you back some cable back at the clamp and ensure no driving on the pull-back.

thanks..I got the plastic pc...almost bought a new belt but will hold off. No sense in repalcing the cable then...?

Plastic pc on in 2 minutes...works fine....thanks!

Ba-da-bing!