Can't Get Past Through Windows Startup

It's a newly built computer with a fresh copy of Windows 7 64-bit. I'm running a:

-Radeon HD 7970
-i5 2500k
-2tb hdd
-asrock extreme4 gen3 p67 mobo
-16gb ddr3 ram dual channel
-1200watt psu
-nzxt phan-002 green case with all working fans

The problem I'm having is that whenever I boot up my computer, I can't make it past either the Welcome screen on the Windows login or past the actual Windows startup itself. I'll either get a black screen directly after the Welcome screen or my desktop will load, but I will find that if I click on anything, everything freezes up and I'm forced to restart. It has been intermittent at times, and I have actually had "good boots" where I could use my computer as if nothing was wrong... But that seems to be very random. This problem has been plaguing me for about 5 days now. And after much persistence, forum-browsing, and troubleshooting, I'm coming here to seek advice.

It all started when I uninstalled my ATI 12.2 video card Drivers and the ATI Catalyst Control Center. I intended to reboot my computer and install the new 12.3 drivers. The login/startup problems all started from there. I tried a multitude of things:

-restarting my computer.

-unplugging everything and plugging it back in (all the cables had worked flawlessly for over a month for moderate-heavy use per day)

-reseating my video card

-trying another video card in my computer

-in fact, an nvidia card, and had gotten the nvidia drivers (which are now totally uninstalled and swept clean with Driver Sweeper) to work, and had a couple good runs... But even then, it wasn't a for sure deal as the startups were sketchy then. and upon reinstalling the hd 7970 and new drivers, also a few good startups, but the problem persists.

-checked the bios to see if all my hardware was being detected properly

-checked for drivers for my motherboard

-checked ati's web site to make sure i got the right drivers

-used safe mode to do a LOT of troubleshooting, such as:

-scanned my computer with a complete scan with both avast and malwarebytes, and now also superantispyware. (found a few tracking cookies that were removed, but the bad startups still persist)

-ran system file checker tool and found no problems

-ran a chkdsk and came up with no errors

-uninstalled everything i installed that same day (two games)

-scanned the games setup files that i installed, thinking they were infected, came up clean.

-tried to uninstall the ATI drivers and attempt different fixes, but in safe mode, can't uninstall OR install ATI drivers, even with edits to the registry or via command prompts

-uninstalled the ATI drivers from the device manager and this seemed to help a little, but windows was still inconsistent

-used system restore to restore to a point BEFORE i uninstalled the drivers, but the problem persisted... That really threw me for a loop.

-the ONLY thing that worked, even momentarily, was when i tried Last Known Good Configuration after having installed the nvidia video card. it worked for a moment, but things were still loading slowly and wasnt standard operations. bad startups persisted soon after.

i've done lots of stuff to try to alleviate and see what the problem was... if i remember anything else i did, i'll let you know, but that's everything i can recall at this moment. for the first few days, i thought my computer instability was because of the ATI driver malfunction, which could be true... But now I'm thinking it's more because of an error lurking within either explorer.exe or the login process itself. because i could get sticky keys to pop up amidst the black screen of death earlier, and with zero input lag. got the sticky keys to pop up again when my desktop appeared on one semi-successful startup... but upon opening any folder, or clicking anything at all really, everything goes to *** and lags out till i have to restart. i want to avoid having to reinstall windows at all costs. i am not one for giving up unless ALL options are exhausted, and i feel i have yet to do that. I have a lot of information on my computer, most of my 2 tb are full of things. entertainment for the most part, but took a while collecting from various sources and dont want to have to rip them again and whatnot, as the hard copies are scattered about with friends.