Bug Check 0x19: BAD_POOL_HEADER
This indicates that a pool header is corrupt.
In this case:
Parameter 1: 0x20
Parameter 2: The pool entry that should have been found
Parameter 3: The next pool entry
Parameter 4: Reserved
Cause of error: The pool block header size is corrupt.
Points to HDD/RAM. Run memtest86/Prime95 on each stick of RAM to ensure there are no errors then report back.