I'm trying to repair a friend's Compaq Presario C300, but I have a feeling the hard drive is completely dead. When you try to boot the pc, you get that screen telling you the pc was shut down incorrectly and asking which mode you want to start it in (safe mode, COMMAND prompt, etc), but no matter which you select, it simply restarts and repeats the same process. I was able to get it going using a boot diagnostic disc, but was unable to locate any of her documents, which led me to the believe the hdd was gone. I then tried to just do a clean reinstall of windows and got the message that there was no hard drive located, which sounds pretty definitive to me. So anyway, other than what I've done, is there anything else to check to make 100% sure the hdd is bad?

Also, I've replaced hard drives on desktops before, but never in a laptop, is it pretty much the same process?Hi,

No its not the same as Desktop, Removing Harddrive is very much different in Laptop as compare to laptop.
you can do one go to google & check how to remove itIt very much sounds like the HD is dead but when you say that you were "unable to locate any of her documents" were you able to see the hard drive (i.e. C:\)?
Also, you could take a look in the BIOS to see if its viewable there.

I'd take the drive out and make sure there's nothing loose of visibly wrong. Although different to a Desktop, it really no harder to replace, just make sure you get the same physical size and type of drive. Here's a manual with details on how to take the drive out Section 5-7 to 5-9.
h t t p://h10032.www1.hp.com/ctg/Manual/c00753552.pdf

Take the spaces out of 'HTTP' above before copying it into a web browser. Of COURSE it depends on the laptop, but replacing anything on a laptop is similar to working on a desktop, EXCEPT, taking a laptop apart ( and putting it back together) is a lot harder due to the size of the components, and how they are crammed together.

Working on a desktop is kind of like being an auto mechanic, while working on a laptop is more like being a watch repairer.Here is a suggestion.
First, carefully open up the laptop and find out exactly what type of drive it has in it. Many of the older laptop hard drives are 2 1/2 inch drives with the connector that looks very much like the standard IDE connector, but there is no power connector. The power actually goes through the connector that looks like the standard ribbon connector. If so, then you can find replacement drives available from the major vendors on the Internet. Also, you can buy an adapter that converts the 2 1/2 inch laptop drive to the standard connector used on many desktops, the IDE connector. Most desktops still have IDE connectors inside, so you could hook up her old drive to the adapter and with the proper cable plug it into a desktop turn it on and see if the operating system will recognize a second drive in the system. Just possibly you might be able to recover some of her DATA. Hard to say.
Anyway, having an extra laptop drive an adapter cable is a good investment. Very handy thing to have when friends ask you to fix their laptops.
Update time:

I decided to replace the HD, she wanted the largest one available, so I purchased a Western Digital WD5000BEVT 500gb drive. I removed the original drive and installed the new one, but now what? When I try to install Windows, it tells me there is no drive. I figure there is a driver set I probably need for the computer, but I haven't been able to find anything specific. I did find a list of drivers on the Compaq SITE and downloaded them all (not sure which ones I needed), but when I made a bootable disc with them, a bunch of DOS text comes up, then I get the message "Search for USB HDD Devices... USB support successfully initialized... No NTFS volumes found, exiting..."

Any suggestions? I've replaced desktop hard drives before and never had any problems, though those always came with driver discs. I checked Western Digital's site and they say "Most WD drives do not include drivers because they use a standard driver built into the operating system".

Help! I think I got it. Per what I read here http://www.mydigitallife.info/2007/10/23/windows-xp-setup-could-not-detect-and-find-any-sata-hard-disk-drive-on-ahci-mode/I went into the BIOS and disabled SATA and now the Windows install seems to be proceeding normally. Keeping my fingers crossed...