Vista Start up error

Hi all...

Got some problems with my gaming rig, and it seems a bit wierd. System Specs first:

Q6600
Ati 4870 x 2
Catalyst 10.4
Win home Vista (32 bit) SP2
4 gb ram

The problem is when I switch on the computer, after the POST and after windows start loading but before I get into desktop, I get a black screen. Subsequently it does not load into desktop. Believing that the computer had hung in the process, i;d reset the system. I'd go into safemode, and then restart the comp from there -- and the 'problem' gets solved. Once I get into windows again, subsequent restarts do not trigger the black screen. The black screen therefore only triggers after ive switched off the computer for an extended period of tme ( like a couple of hours).

Been googling a bit, and thus I've done the following:

-Checked power cables (tried system with diff power cables)
-Reseated my Vcard in case this was the issue.
-Ran chkdisk (left the comp on and let it chk on its own and repair it -- came back after a couple of hours to see it booted in desktop, so I think it cleaned the system)
-Ran Anti Virus/ Malware programs (nothing detected)
-Run mem test for 1/2 a day, there are no errors despite over 1000% coverage.
-ran this http://support.microsoft.com/hotfix/KBHotfix.aspx?kbnum... but it did not help.

What I'm thinking of doing:
-rolling back 10.4 to something else, in case that is the one causing the problems.
-checking the RAM to make sure it is seated properly
-Thinking of formatting HDD soon (probably over the weekend/friday), but just worried that the problem lies with a hardware rather than software. But if I do format, I'm still considering if I should update to Win 7, considering I can get a 64 bit system that actually *recognizes* my 4 gb ram.
-checking the battery, but worried i may possibly damage the remaining system.



I'm not sure how to solve this problem, and not sure if this is a hardware/software issue. Would love suggestions.

Note- At this point, this problem is an annoyance -- I still can get into windows (via safe mode, and restarting work around) -- but I'd still appreciate a solution to remove the problem completely.

Thanks for your time for reading and replying.