NTLDR is missing

I have Windows Vista, and it's a Dell desktop with an Inspiron tower. When I turned my computer on it said "NTLDR is missing; press any key to restart." I pressed space and it said the same message over and over, but finally I pressed another key and it started up. I am totally bad with computers, can someone tell me what this might mean? Do I have a virus and how can I get rid of it?

And there weren't any disks or floppys in there.

Vista does not use the boot.ini. But XP uses the NTLDR, which indicates there is an XP installation lurking there. Does anyone else have access to the PC? It sounds like an abortive attempt to install XP has occurred.
But, if you have a Vista DVD, boot up on it and (after you have put your language etc in) select repair startup, option.
If this does not work try some of the fixes at this link:

NTLDR is missing, press any key to restart - Tech Support Guy Forums

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