A bad sector on the hard disk is a bad thing. It might be time to replace it. But I doubt if it is related to the message about pressing delete, although that might depend on where on the hard disk the bad sector is located.
The message, as you describe it, seems to come from the BIOS, not from Windows 98, so this might be a little bit the wrong forum. If no good answer turns up, you'd better contact Dell technical support, in my opinion.
When i booting up my pc, it asked for 'Press <Delete> button to resume' after the hard disk detection. My current o/s is win98, Intel Celeron (Dell Bios). I need to press <Delete> button all the time when i bootup my PC. When i run scan disk, it found bad sector.... Help...