checkpoint (HDsk) Alert! What does this mean?

I just got back from a vacation and after I used my Dell Dimension 4600i Series (BIOS version A09) for a few minutes the screen went blak with a message stating SATA PRIMARY DRIVE 0 NOT FOUND STRIKE F1 KEY TO CONTINUE, F2 TO RUN SETUP UTILITY. 

When I try F1 it states NTLDR IS MISSING. PRESS CTRL+ALT+DEL TO RESTART. When I do that it goes back to the same original message.

When I do the F2 it lists the time and date and lists

DRIVE CONFORMATION----------ENTER

DRIVE A.............................3.5 INCH, 1.44 MB

SATA PRIMARY DRIVE....UNKNOWN DEVICE

SATA SECONDARY DRIVE ....OFF

etc

after doing the ctrl+alt+del several times I got a message stating ALERT! PREVIOUS ATTEMPTS AT BOOTING THIS SYSTEM HAVE FAILED AT CHECKPOINT (HDsk). FOR HELP RESOLVING THIS PROBLEM, PLEASE NOT THIS CHECKPOINT AND CONTACT DELL TECHNICAL SUPPORT.Can anyone help me with this? I do not want to spend alot of $ on this but yet I have a lot of info on this computer that I cannot lose. Also, I am not a computer person so any help will be greatly appreciated.