The blinking question mark is not the only symptom of these problem hard drives. Nor is it the most consistent. The problem drives also register as "not initialized" when you look at the drive using Drive Setup, even though the drive has data and the computer is able to start up and run with no problems. I know it sounds unbelievable but we had over 1000 of these hard drives that came up as not initialized.
The problem drives are from Seagate and have a firmware version of 1.35, 1.37, and 1.38. We bought over eleven hundred 5260/120 Macs in the last 7 months and over one thousand of them had the problem hard drives. Many of our computers never experienced the blinking question mark problem. Only one of these bad hard drives lost data.
Fortunately Apple is replacing our hard drives."