Help with 9800 PRO

OMG this thing is making me angry, i need some help. first i uninstalled all drivers for my Nvidia GEForce Fx 5200. but one cannot be removed from my harddrive for some reason. i go to add / remove programs. so i went to safe mode and used Driver Cleaner. still there. i deleted another nvidia driver but the other wont go away. so i put my new ATI 9800 Pro in and connected it to the harddrive and power supply. there are 2 power supply things one says P6 and the other is P3. does it matter which i plug it into? whenever i turned the comp back on i heard a LOUD humming noise so i quickly turned it off cuz thought it was gonna blow up. i have no idea what the problem is. i dont know what my AGP is either, if it is a 8x 4x 2x... the manual said to update drivers for the slot first but i cannot find out what chipset/motherboard i have. i dont know how to locate it on my computer. If some one could plz help me i would love it soooo much. thank you!

ps: if i have pc 2700 ram can i use it with pc 3200 ram at same time?

specs:
emachines w4685
p4 2.6 GH
512 Mb ddr
300 watt or more powersupply cant remember

 

I use "Detonator Destroyer" that I downloaded from http://www.guru3d.com I used it and it wiped any trace of my old NVIDIA drivers off my PC.

 

oops Try NVCleaner. I haven't used DD since I upgraded and I see that XP is not supported.

 

driver cleaner 3.3 is reccomended by BFG tech support when removing older drivers

 

the loud humming noise is probably due to a dirty fan or a wire is rubbing against the fan ... try an air spray can on the fan or moving wires away from any fans in your case ... and it doesn't matter which power connector(p3 etc) you use so long as it has the standard 4 red/black/black/yellow wires , most likely it does ...

and you can mix 3200 w/ 2700 but they will run at the 2700 speed so to save money id just go with 2700

i would use the driver cleaner after you install the 9800pro .. then install the radeons drivers

 

i got my pc to work then i played doom 3 for 2 hrs yesterday. today i played doom 3 and the framerate got slower than it was and my computer shuts completely off a couple of minutes into the game. what is its problem>?? plz help