First of all, does the BIOS screen come up at all?
If it does, what does it show for installed SCSI disks or RAID controllers? Is there more than one HD physically in the box?
If there is only one, perhaps someone salvaged the other disks that were formally in a raid-5 setup - one disk will not boot - 2 is the minimum that can recover from the 3rd disk missing.
If the machine had sat around unplugged for a significantly long time, perhaps the NVRAM battery has completely discharged. Maybe just leaving it plugged on for several days will cure the problem. Perhaps the NVRAM battery is just plain bad, and replacing it will fix the problem.
Finally, check with HP. Maybe the box is still under an extended warranty.
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Pat Welch, UBB Computer Services, a WCS Affiliate
SCO Authorized Partner
Microlite BackupEdge Certified Reseller
Unix/Linux/Windows/Hardware Sales/Support
(209) 745-1401 Cell: (209) 251-9120
E-mail: patubb@inreach.com