перестал работать бэкспэйс в vim :-(

stty -a < /dev/`tty`

This will show the mappings for the current tty (terminal basically)
Look for DEL=
It should say ^?, this is the control character shown when you hit Backspace.
Try to do this to make sure it is recognized correctly:
stty erase ^? (Where you actually press the backspace key rather than type ^?)
Then try to start vi again. Btw, are you using vim or vi?