Stability Problems PLEASE HELP!!!

Hi guys..i hope so much you can help me... (sorry for my english im from argentina)
This story started like 2 months ago...
I was using win ME and everything was right..i had no problems, and suddenly..I started getting errors with .dll files.. like rundll32.dll opera.dll etc.....for example I tried to run any program and a few minutes later, or just in the moment when i launched, it crashed..
i thought it was some kind of Virus..so Formated the hd...
Then tried to install winME again..instalation copied all the files, rebooted..and then when it started windows for the first time and check my hardware the plug and play etc...it crashed...Cmdnist made and error with rundll32.dll and similar, it was the same problem, but i couldnt even install windows this time....what kind of virus is this i thought!!!??...so I gave the Hd to a friend that knows alot of this things, and he formated in low nivel, deleted the boot record of the disk, and did all the things he could...but I got the same again!!
so then I tried installing win98..it worked, i could install it fine...and now im using it..but i have the same inestability i had before, i mean, programs crash all the time, problems with all kind of dll and all kind of aplications..i have to reboot my pc every 10 minutes it sucks...
I thought this very smart virus was still on the hd, so I tried with diferent hd...but it wasnt the hd cos i got the sames problems with any disk I tried...!!
and then I opened the CPU and cleaned everything, checked the RAMs memorys and saw all was right, it should works fine..but it doesnt..

isnt anyone having the same problem?? all i can say now is my pc is PIII 533 133x4 2 ram memories one 64mb another 256mb 15gb hd maxtor and mother soyo...the modem is motorola sm56 and the video card is gf4 440...

what should I try?? im Crazy im desesperated i cant play my favourites games...sometimes i open the games and then it just go back to desk and close the aplication, sometimes i try to change monitor's resolution and it craches... please really...i cant believe whats hapenning please HELP!!!...i did everything i know...help....
Thanks to everyone that opened my thread, really thx

 

(Please excuse my English, I'm from Australia )

If it's doing it on both operating systems, then it's either hardware, or software you have installed in both o/s's.

Do yourself a favour and forget about ME if you have 98. ME is more problems than it's worth.

Start with a fresh install of 98, with the minimum hardware you need. Don't install extra software until it's stable, and then only do so one at a time to find the culprit.

To check hardware, you can use the programs like SiSoftWare Sandra and/or Dr Hardware.

Also, Windows has a diagnostic tool called Dr Watson.

HERE is how to use it.