As slomacuser suggests, the drive has probably failed its startup self-check. Prudence says that you need another drive, but the old one is not necessarily all Gloom and Doom yet. If you have an external SCSI enclosure to which you can remove it, you may, after several careful startups, each separated by a little rest time, be able to pass the startup hurdle and get hold of the drive long enough to get your data off. It may even need a disk utility other than Apple's to do so: LaCie, FWB, InTech, ATTO, whatever, depending as it was the mechanical check or the memory check that failed. If the data were of no consequence to you, maybe just a funeral with military honours is needed.

If it is Winter wherever you are, make sure that the drive is at 15-25°C before you press it hard to perform. It has been known for a lateral blow with the heel of a hand (firm, but not excessive) to free up a drive that was previously disinclined to behave. Yours already spins up, however, and is seemingly disinclined to continue rather than disinclined to begin its business.

de