|Very carefully - use the XP CD and run a repair installation - as per this link. Read the info at this link very carefully so as to fully understand just which "version/type" of Repair routine you use... |
Pay close attention to steps 3, 4, and 5.
Also can you boot to safe-mode - and if so is the desktop etc. still missing?
You're obviously (and understandably) concerned about your data/files etc. Might be a wise move to get a Linux variant on a CD (Knoppix or Ubuntu); boot up with that and then copy off all data etc. to optical-media... Verify those copies are truly accessible on at at least one other system too.
Both variants can be downloaded as an iso and then burned to a CD; boot up etc. with that CD...
Once data is secure... then set about resolving your present dilemma as above (via a Repair Installation)?