OK, so here in the office we got another PC about two months back (not newest, but it works). Since I'm the resident tech expert and only I didn't have a piece of hardware assigned, I got that cuckoo's egg.

Now, the first Windows installation came out about well.

Before that, I found traces in BIOS that someone tried extreme overclocking (400 Mhz @ 533 Mhz -> 30%). The FSB speed and multiplier are both BIOS-controlled. I returned the multiplier to a normal value.

It worked about well for a month - one BSOD per day max, and some PC's here did worse, believe me. Then the trouble began. System barely ever booted without problems (once I did, like, 12 reboots until it started up without greeting me with a BSOD right away), BSOD's popping up like mushrooms after rain, the onboard LAN constantly corrupting data and so on. Once I have tried to calculate an MD5 checksum for one of the stored files - and repeat it just in case. I hoped I'll end up with 3 to 5 checksums, and two or more will surely match. Right. 12 checksums, no two were the same.

I guessed some of the problems might have something to do with the motherboard overheating, so I went and did a couple things about that. New application of thermoconductive paste to the CPU, several extra fans attached and removal of the casing, to be exact. The fans have neccesitated using a separate PSU in order to power them up, but that wasn't any issue - we have still almost half a dozen of working ones.

I know that the motherboard isn't too good, actually it's one of the less stable types out there (PcChips M748LMRT), but the sheer number of issues popping up forced me to make a backup of the data stored on the drive, formatt it and reinstall Windows (and all the other software) from scratch (not to mention that it got effed up anyway after a couple attempts at saving the damn thing). Or, at least, attempt to...

Out of the frying pan and into the fire. Now I found out that the PC began critically glitching even during the _installation_ of Windows (It's 98, BTW, since that machine can't bear a monster like XP). In the end, I found myself unable even to install the OS again, and the boss refuses to acknowledge that the problem exists (every time I tell him of this, he says something along the lines "You're the IT here. Go solve it.").

So, I ended up here, asking for help. What can be done to get this bad boy up and running, except for completely changing the motherboard (if I had one / could afford one of my own money ATM, I would have done that already)? Please...

Have you tried swapping the memory and any add-on cards such as graphic cards, when overclocking, these device can also be damaged because they depend on the FSB.

a memory test would be my idea as well.

I have also run into trouble while installing winodws after having issues. turned out to be bad sectors on the HDD. Do a chkdsk

Memory and processor check IMHO...

-HDD's checked on other PC's. Working.
-GPU's one from my own parts cache. Not compatibile with some hardware, but with this PC it actually worked.

Will check about the RAM, right now I'm a bit p*ssed off as it turned that my ISO of UBCD was corrupted, so I'll have to redownload it.

Version 3.3 of UBCD is a bit buggy, it's better to use version 3.2

UBCD 3.3 used, could not obtain 3.2.

Turned out that two of the RAM sticks were faulty. This cuts out 64 of 96 MB.
The CPU isn't too perfect by itself, but mostly passed the test (1 error total, not bad that).
Will buy a new RAM stick out of my own funds tomorrow.

well did you get new ram sticks

Yup. And then I re-installed the f***ing Windoze anyway, just to make sure. Then the obligatory course through Windows Update.

After this was done, I started the computer for a data download on Friday evening. Now it's Wednesday noon here, and it's still running - it didn't suffer even a single crash or error since then. No resets, reboots or power-downs.