BIOS Not Detecting Primary IDE Master Drive

Dell 4500 2.4MHz P4, 1 GB RAM, Win XP Home, Maxtor 40GB HD (In service since 8/2002)

First off, yeah I know, old drive but I already have replacement and plan to install soon but suspect this problem may prevent success.

Recently opened tower case to clean, compressed air, new small paint brushes, vaccuum. Disconnected data and power plugs from all IDE drives (master HDD on primary, DVD player and CD-R on secondary IDE).

Upon reconnect and power up, got following message (paraphrased) white ASCII text on black screen "Switch boot device or install bootable media."

\Powered off, checked connections, tried boot again, same message.

Inserted Dell Resource (XP Reinstallation) CD, observed what appeared to be loading of device drivers in memory, then presented with options (reinstall XP, repair XP, do nothing and exit). Attempted repair...dead end. Explored reinstall but want to save user files if possible before wiping drive. Then something unexpected happened.

Upon exiting XP installation (remember, did nothing but appear to load device drivers in memory) Windows booted up and everything seemed to work.

Next day, got same boot up message as above. Powered off, rebooted but invoked BIOS (F2). It was there that I noticed that BIOS was not detecting any drives on the Primary IDE. However, upon exiting and not saving BIOS settings, machine booted up.

I have tried swapping IDE data cables using the one that came with new drive Seagate Barracuda 200MB, 7400 spin, 8MB cache IDE) I will be installing to replace the 6 YO Maxtor 40GB, 2MB cache, 7400 spin. Still got error message.

So, is HD defective somehow (perhaps the boot sector?)

Is Primary IDE interface on MoBo bad?

Or, and this is something that just occurred to me.

I noticed there was no jumper connected on drive. Can't recall if one was one when I started cleaning, guess it's possible it came off and got vaccumed up (can't believe autocensoring forced me to remove the word usually used to describe a vaccuums action). Wasn't concerned about its absence though since BIOS is set to ID master drive by "cable select" and I figured a jumper setting (i.e. connector) was not necessary for cable select. Am I wrong about that? Should HDD (especially boot drives) ALWAYS have a jumper connector even if BIOS is set to cable select?

BTW, I'm not trained nor especially versed in PC maintenance, but I'm quite intelligent, can follow instructions and comprehend tech references pretty well, and hence am a pretty decent diagnostician for being untrained. I'm probably the equivalent of a shade tree mechanice in automobile speak.