The first thing I would do since the hardware has been moved around alot is boot up into safe mode and go to Device Mgr. Click the plus marks in front of all of the hardware (except System category) and look for duplicate or multiple entries under each category.
If you find any, remove ALL entries for that piece of hardware not just the duplicates and reboot the computer. Windows will again find the hardware and only put one entry back in.
Then get out your motherboard cd and reinstall all of the drivers from that cd. I would think as far as no beep goes when you boot up since you're not having any 'problems' that you probably bumped the connector loose from the pin(s). I actually have had a couple of boards that gave no beeps ever on boot unless something was wrong like the ram or video card was an issue, but since yours beeped before, a loose or disconnected pin connector is probably the answer.
System: 5 year-old PC: Win98SE, Pentium II 350Mhz, 184 RAM
Drives: Quantum 30GB, HDD Seagate ST-340015A 40GB, HDD Quantum 3.2GB (in no- name removable drawer); LG DVD/CD-RW ROM
Motherboard: PCChips M748MR-spec/Xcel 2000; AMIBIOS 62710 (Burn-in 24 HR AMIBIOS 1995 CY 4621
Modem: Terayon cable with a non-networked computer (pc #2) sharing a Linksys BEFSR 41 Router
Ethernet adaptor: D-Link DFE-530TX
Other: 70 programs in Start Menu.
Background: Recently I installed the Quantum 30GB, the Seagate 40GB and the Quantum 3.2GB (removable drawer). Tried many configurations before getting drives fully recognized, lined up and working. During that process, I ended up with these problems: (1) lost the single **OK** beep from BIOS post; (2) the three PCI expansion slots no longer work; (3) no LED on D-Link adaptor; (4) no internet connection and; (5) nothing re: D-Link adaptor shows up in Device Manager.
I probably fried or disturbed something on the motherboard. However, all other programs seem to be working.
Self help: This Forum and Google gave me several repair ideas. Electrical troubleshooting beyond my skill level but I did reseat the memory as well as the D-Link and did a general check for loose connections and debris. Tried a functioning ethernet adaptor card in each PCI slot ? no luck. Verified BIOS enabled for Plug&Play but new hardware not recognized. Manual attempts to re-install the D-Link adaptor driver programs end up with a message to ...**shutdown the machine and install the adaptor**. At the moment the D-Link adaptor is in PC#2 and working just fine.
Questions: No problem if I just ignore lack of BIOS **OK** beep or will other problems showup? Any way of getting the PCI slots working again or do I need a replacement mother board? I'd sure like to hang onto this old PC for a while longer. TIA for any ideas or comments.