Plug and Play configuration error in Dell Dimension 4300S

I do not know the history of this machine except the client called me when it would not bootup.  My assessment was that it would boot, but could not find the HD.  I put an old drive into this machine, and it booted OK.  Original HD was not recognized in another computer so it appeared to have failed totally.  Dell supplied me a replacement 80 GB drive for the old 20GB.  The jumper is cable select, and at bootup the drive is recognized.  I then used the Restore CD (newly supplied from Dell) to install Win XP with SP 2.  Now at bootup there is this PandP error message.  I have replaced the MB battery - but get a message battery voltage is low!  RAM seems to be recognized, but I noticed it is not original - and the two modules are from different suppliers.  Other than the HD I have not replaced any hardware.  BIOS shows IRQ5 reserved; all others, available.   After pressing F1 to continue, Win seems to be installing.  Might mismatched RAM be the source of this problem?  What else do I look for?
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Holy cow... that was a smattering of completely different, unrelated errors!
Let me attempt to address them all individually..
1. the battery has nothing to do with your PnP error, however I think there is more than just PnP going on..
2. it shouldn't matter if the RAM is from the same manufacturer, only that they're within 1 step of the same speed (e.g. 400MHz will work with 333's, 667's w/533's, and so on)
3. rather than just "plugging in" the original hard drive, you should run a DFT on the original; HDD's aren't inherently transferrable from one system to another without a few tweaks
4. if you believe the RAM to be at fault... run a MemTest; simple and you can walk away from it :)

so.. onto what I would do with this system...
I say strip it down to just the board/cpu NOTHING ELSE... see if you can atleast get a system beep message telling you it has no RAM.  If that works, go on to installing the RAM; do NOT use your questionable RAM; use known GOOD RAM.  If the system boots fine from there, go into BIOS and note the few important settings. thereafter, install each part as necessary.  I've had many machines work from having done this when it's nearly impossible to find the cause of the error.  Just test all of your parts (DFT the HDD, MemTest RAM, etc.) and do NOT use your own parts when trying this diagnostic--it defeats the purpose.  If all else fails, sounds like a bad motherboard; check your caps for distension and chips for burns.

Sorry for the verbosity, hope this helps!

Are there any pci cards on this PC, try removing them and see if the P n P error goes away. If it does then one of the cards is having a problem getting setup on startup. Try changing slots for the card.
The battery issue seems like either the contacts in the battery connector is not making contact, or the traces to the connector on the motherbaord are bad. Check the connector is contacting the battery and that the battery is in the right way as per + and - . One thing that may be happening is if the power is removed and the battery isn't holding power then the BIOS settings are set back to default giving the problem over and over when power is removed.
As far as the ram being different, I don't think that would be a problem as long as they fit within the specs for the 4300s

Here are the ram specs.

Memory capacities 64-, 128-, 256-, and 512-MB non-ECC SDRAM
Minimum memory 1-64 MB
Maximum memory 512 MB
Memory type PC133 (non-ECC)
WalterOBAuthor Commented:
I took the new battery out momentarily, then in reseating it I twisted it around a bit to be sure it was making good contact inside the plastic housing.  The only cards were a NIC and a modem card mounted inside a housing with a single set of contacts to plug into the MB like a riser card.  I pressed that to be sure it was securely seated.  (Except for the time when someone replaced the original RAM, I think the case had never been opened since shipped.  There was a lot of accumulated dust.  Every fan had blades coated with debris.  I was able with compressed air and a small brush to remove most of it.)  Upon restart the PandP config error no longer displayed!  I then proceeded to rebuild the OS with the System Restore disk, downloaded the drivers from the website, and the machine seems to operate normally.  I replaced a 128MB RAM module with a 512MB (from Dell) so the machine now has a Gig of memory.  I think I was not entirely clear about why I connected the original drive from this machine to another (working) computer.  I used a USB adapter kit to see if another computer would recognize there was a drive at all.  Since the drive was not found by the BIOS in the computer where it was initially installed and not recognized by another computer, I concluded the drive was defective and needed replacing.  Thanks to bsgrim for putting me on to DFT and to sparkmaker for the comments about the CMOS battery.  Now if the machine's user could just remember what the passwords were for e-mail and utilities!  There are no written records to be found.

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Windows XP

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