Sounds like you blew a fuse.
Go here: http://www.mesaboogie.com/manuals/F-Series.pdf
It uses a 2 Amp SloBlo style fuse, you can find then most anywhere electronics are sold.
Now on to the bigger question, what caused the fuse to blow?
You can read up on the tube problem diagnosis page in that manual if you wish which I recommend, however for the sake of the thread I'll mention it.
I would get a few extra fuses, I got two packs of 4 each so I had 8 to mess with (great to have along with a spare set of tubes). Put a new one in and put your amp in standby.. watch all the tubes closely. Then, flick your amp out of standby and watch for any tube shorting. It looks like a blueish lightning strike inside the glass, you will most likely blow another fuse doing this but you'll find which tube is shorting your amp.
Fuses blow when there is a short in the amp in order to protect it. This is usually more often than not a power tube failure.
Good luck, let us know if you have q's