I have a pretty old (>4 yrs) Dell Dimension 4300 which worked fine till a few days ago. All of a sudden, with no changes made to the hardware or software, it regularly (in about 50% of the cases) didn't boot anymore. It shows the Dell logo and then it says "Primary drive not found." before it should show the Windows splash acreen. I then have the option of hitting F1 to continue, or F2 to go to a configuration utility. If I hit F1 it sometimes does boot, sometimes not. If I look in the BIOS (version A06, newest as far as I could find out) I usually see that primary drive 0 (and other drives too) is not configured (usually "OFF" or "Unknown Device"). If I set that back to "auto" (-detect) it sometimes reboots without any problems and sometimes it has exactly the same issue. At one of the good boots I run an extensive chkdsk. No errors were found. I've deconnected and reconnected the IDE cables, no avail. Anyone has any idea what might cause this?

Did you deconnect and reconnect the power cables, or try new cables ? Also, I would run the manufacturer's diagnostics on the hard drive.

You mean the power cables of the drive? No, didn't try that. Will do that tonight. I cannot find the DELL diagnostics disk, so I cannot try it. From the above I can tell that you suspect the drive after all. How can it pass a chkdsk then?

Yes, I meant the power cables of the drive. I meant the hard drive manufacturer's diagnostics, which you should be able to download.

The hard drive initialization procedure seems to be sporadic. If it goes OK then everything is normal. If not, you get the errors. When it boots OK I doubt any diagnostic program will detect a problem. If it doesn't boot then you can't run a diagnostic. Check that the drive data cable is in good condition and firmly attached but the problem is almost certainly with the drive itself.

Thanks for all the answers. In the meantime I tried to disconnect and reconnect all the cables to the drive (they seem to be in good shape, but how do I know for sure?). No change. Also the percentage of good boots seems to be lessening and I even got a BSOD a couple of times when it had booted well at, what seems to be, random moments. I'm afraid it is my disk and I will try to buy a new one and see if that will work.

Well in the meantime I installed a new harddisk and all the problems were over. So I guess it was the disk after all that caused all the problems. Thanks for all your help!