Audio Systems: Subwoofer does not play at high volumes, summer thanks, ohms

Question
I installed two Rockford subwoofers along with a Pioneer amp in my car last summer. The subs were working fine, then I started to notice that the subs would cut off when the volume on the cd player was high. I looked at my amp while this occurred and surprisingly the amp was still lite up indicating that it was on. Any ideas on what the problem can be? Do you think it has anything to do with how old my cd player is?

Answer
hmm.  so the subs cut out but the rest of the speaker (like door speakers) keep playing?
does the amp have a "protect" light or some kinda light that indicates a problem or something?  and if so that never comes on?
what do you have to do to get your sound back?  do you just have to turn it down or do you have to shut the system off and turn it back on for it to work again?
are you sure you matched the ohms of the subs right to the amp?
is this just recently that it started doing this, even with the same music you listend to last summer and at the same levels you listened to last summer?

thanks!