dvd's play fine; cd's sometimes don't load

Frustrating. Moving the cd sometimes is enough to make it play.
The first thing to do is to clean the laser assembly. This can be done using one of the CD "cleaner" discs or (carefully) by hand using Q-tips and, perhaps, a dab of alcohol.

Give that a try first. If it works, great! If not, you may need to have the laser assembly realigned for proper focus. This is usually a job for a qualified technician...

How old is your disc player? Ag5ee With RW re the laser assembly. I have had a couple of CD players that had reached that have died a more or less a natural death and were irreparable. If you have a really good CD player that can be fixed go a head but bear in mind the diminishing returns.
So RIwainwright, a dirty laser could read dvd's perfectly but have difficulty with CD's?