Bay door lock will not open the bay

Since the key is turning but the latch isn't, I rather doubt my pressure suggestion will do much good. I hope I'm wrong, of course.

If you can get in from the back, you may weell be able to unbolt the latch from the lock cylinder or, failing that, cut off the latch tongue with a rotary tool or something, assuming this is a quarter turn lock (and not some sort of a locking paddle latch or other more exotic design).

Pretty much sounds like you'll have to come in from the back side. My guess would be that the key barrel has come loose from the locking mechanism. May have to replace the whole thing, not much of a deal.

The key turns in the lock but it is still locked, I think. Gonna try Drew's suggestion and use a little pressure. May have to crawl into the bay and take a nap while there.

Do you mean the key/lock combination won't turn, or does the lock turn but still won't open?

Sometimes my locks stick a bit due to the locking tongue thingy being somewhat tightly wedged against the door frame. Applying pressure to the bay door so as to give it some wiggle room helps in that case--which generally means pushing inwards somewhat.

WD40 isn't a great lubricant for locks; dry graphite powder (or something similar) is typically recommended. The dry preparations don't tend to hold dust and crud in place as much.