If the MD5 check fails, a few things could be at fault:
1: Disk is damaged [that being said, you'd usually get an error during the install, and not a MD5 failure]
2: HDD has bad sectors [unlikely, as SMART should pick up any HDD related problems]
3: Bad memory [possible]
Run a memtest scan, just to be safe. Essentially, something is broken somewhere in your system, as you should never see a MD5 failure during an install.