Brakes locked up. Need help!

Betcha the piston in the master cylinder is pushed in too far and won't come back enough to release the fluid back into the master cylinder.
You can prove this easily by loosening the master cylinder to booster mounting bolts and the brakes should release.
If this is the case you have a few choices to fix it.
1. Back off the brake push rod
2. Get a shorter push rod
3. Space the booster and master father from the firewall.

I'll bet your pedal is at full up and tight when this happens right?
Make it lock and then loosen the master cyl bolts and if that is it, then it will probably make sense.

:D Typing at the same time, but at least we agree.
That ought to make the OP feel better.