try a fresh install and see if the problem still happens before installing any drivers. If not install one driver at a time with a reboot inbetween. Start out with the drivers off the motherboard cd first to install the chipset, intergrated nic (if using one), integrated audio (if using). Then install video drivers. Next install drivers for anyother hardware you have one at a time.
Keep track of when it starts getting slow. Thats the driver or hardware thats causing the problem.
If your not using any onboard devices, disable them in the bios before installing windows.
Second thing to remember and do is to not install any add-on cards like sound, nic, raid - unless booting off it, untill after windows is loaded.
Once windows is loaded and all other drivers are installed then put in your add-on cards one at a time.
Here is a little application that shows you what is actively running in live time it may show you things you may not of known are running in an easier way to decide if certain processes are hanging http://www.nirsoft.net/utils/cprocess.html also check your event viewer an see if there are some errors that may help you fix them its in the control panel under computer management utility.
ok got cureprocess running. it shows 21 processes and 39 modules. nothing seems to be out of the ordinary to me.
Yellow question mark means that the device isnt recognized correctly "wrong driver". For your video its not always the newest driver nor the one that came with the card that is neccesarily the best one. I usually compare online with otjer machines running the same or similar hardware as mine useing 3DMark to get a score whomevers driver gets the best score I try and rebenchmark. You can get it here http://www.futuremark.com/download/
i finally found the correct driver. didnt seem to affect my perormance any, if at all.