Based on what you described, it sounds to me that your system can boot to a grub command line but most likely grub is unable to read your root partition which contains your operating system files.
If you installed using a** DVD **you will want to boot to that and select “Upgrade” which should repair your system.
The “Upgrade” should find your root partition and re-configure so it can be read again.
If this doesn’t work, then you may want to weigh the effort needed to troubleshoot your problem vs wiping your disk and starting over.
Of course, regardless of your decision, you should try to remember what happened that might have caused your problem.
If you installed using other media like the NET install, I’d still recommend you download and run the DVD so that if you suffer a network connection, it won’t leave your system in worse shape than before.