It's not a hardware failure. Some of the 360's from a certain manufacturing line have a memory leak that corrupts the flash RAM. When the patches happen (For any game, not just Guitar Hero) certain 360's risk reaching some sort of threshhold in their flash RAM which causes it to corrupt. In some cases, some folks can continue to use their 360 for awhile, until they hit that memory address and then it dies again.
Microsoft takes the systems back, sends you a refurb, and reflashes the RAM in the old console and sends those back out as well.
This is why some folks get bricked systems 2, 3, 4 times in a row, because they continue to run the same programs on the machines, which causes the flash ram to corrupt.
Although, obviously, in some cases it is an actual hardware component failure. But by and large, the issue is the flash ram getting corrupted.
K