I have a 18 month old HP Pavilion 8635, running Win98SE. Today when I switched on, all I got was a black screen with No operating system found written on it. I have tried booting from a floppy, and the recovery disk, but everything tells me my hard drive is not there!! Is there any help out there please??

I had analog problem with few another Desktop. Problem in contacts of IDE-cables: or mechanics (out off by vibro.), or oxigiing.
You must remove cable from HD & MB (wishing cleaning the pins)& insert back.

Do NOT remove the cas if your machine is still under warranty. If you open the case, breaking the silver warranty sticker that says "Warranty Void If Seal Is Broken", well...nough said.

If you did not install any software just before the problem began, pop in the Windows98 Startup disk, which you should have created either during the new OS installation or upgrade, and then turn on the machine. When you see the Windows Startup Menu, select "Start computer without CD-ROM support". After it has finished starting the computer, at the A:\> type the following command line. SCANREG /RESTORE

Choose the most recent dated registry then choose OK and follow the rest of the prompts.
Remove the floppy when the machine begins to Re-Boot.

I have had similar problems on Compaq machines, here it was not hardware, rather than the compaq ide controller failing to talk to the boot sector on the drive. It seems from time to time that these machines loose it (putting it simply) and the only way to get the drive back, is f-disk and format, (which erases all the data)
I couldnt even get at the data using the drive as a slave, the Drop point was out, and the drive was listed as unformatted.

Another (more hopeful)thing , is if you hit F2 and get into your HP bios , hopefully hp will have left the option in on the Pavilions to Turn OFF the S.M.A.R.T. which is a self diagnostic utility whereas a Hard drive will report when its about to fail.
However this system has been know (on our HP Vectra machines) to be inaccurate, and can cause booting problems.

Hope you find something of help there
Bo

Tried the scanreg/restore..said bad command..tried hitting F2 and couldnt get into bios...just keeps telling me that operating system not found. anything else??? please

You have to press F1 when the HP logo comes up and do the thing that Bo Pedersen told you.

Thanks for all the replies, but at the end of the day, I need a new hard drive, it really has given up the ghost!!!