18 year old VHS tapes?

I was just playing very old VCR home movies and everything looked ok but now there is nothing but snow with sound.
I have two newer VCR/ DVD combos and this has happened to both of them and I don't know whats causing it.
Its not the tape because I put in one video that was ok and now it doesn't play either.
I've tried using a head cleaner but had no luck.
Did I ruin the heads some how?
Is it something to do with a demagnetized head?

First thing to do is figure out whether it's the tapes or the players is the problem.

Do you have a commercial VHS tape? (I assume it's VHS, but same principle would apply to Beta.) Will it play in the players? If so, there's a problem with the tapes, and you may be out of luck.

If the commercial tape doesn't work, you may have to try cleaning the heads several times.