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 openen my thread, really thx

 

I'm wondering if it's time to start thinking about the possibility of a hardware problem. For instance: a flaky memory chip on one of your DIMMs. It happens.

You might try downloading a memory test program from <http://www.majorgeeks.com/downloads26.html> and running that to see if it raises any issues.

Another thought. You're running a PIII 533, so it must be several years old. Over that period of time, computers sometimes try hard to fill themselves with dust, thus setting up temperature-related instabilities.

Make sure that the fins in the heatsink on your CPU haven't clogged themselves with dust, and while you're in there, clean up anything else that has accumulated a layer of dust. If you've been operating in a dusty environment, you may even need to remove the power supply, open it up, and take the dust out of that too. (Don't forget to unplug the system before you do that!)

 

Thx Rob.. i will try what you said, specially testing my RAMS...I really think its possible, thx
you guys please tell me what you know about it so i can fix my problem! =)