hey mnajem , this should help you out!!
Boot Sector Infector
A BSI is a virus that attacks the computer on boot. Sometimes
halting the boot procedure alltogether and/or damaging boot files
making the system either unstable and crash on startup or not
able to start at all. These are some of the worst viruses to
get because once infected you are unable to run system virus scans thru the OS

Bingo!!