Is there any data (personal files - stuff) on the drive that you'd like to safeguard?
If so then the first thing todo is to duplicate/copy it all to external media.Typically DVD but an external hard drive too is nice(r).
If the system won't boot at all and thus allow you access to those important personal files etc... Then download and burn to a DVD a free ISO for ubuntu (ubuntu.com). Boot with that DVD and then you can access the hard drive and al its contents; and thus copy all your files to DVD etc...
Having done that one can safely set about resolving the problem as described?
Second (implied) question; presumably it won't boot even into safe-mode?
Supplementary: do you have full version (OEM or Retail) disk for XP?