Ok, i have seen a lot of people with this problem.
-you would either boot up normally but when you started playing a game or watching a video your monitor would suddenly go to no signal.
-you would see the post and hear the tune for the windows logo but get no signal
-you could boot into windows normally but after about ten minutes you would suddenly get no signal.
so you have checked your cables, reinstalled the drivers, reseated the video card, traded in the video card etc etc...
still the problem persists.
i believe all this happens because your computer "forgets" which monitor is installed and then installs the drivers for the default monitor. once this happens, your monitor can no longer display the resolution you are using and wham no signal.
the reason this happens during games for some people is that when they are not playing games they are using a resolution that is supported by the generic drivers but when they start playing games the game switches to a nice wide screen resoluiton that is not supported.
two things you can try, and unfortunately i didnt do this in a scientific enough way to know for sure wich of these two things actually fixed the problem but one of them did for now at least.
check in your c: drive. if you installed vista over top of xp, (not as an upgrade, but as a full install without actually formating) vista packages xp into a folder called "windows.old" that folder contains all the information about your xp installation. i have a theory that when you install the nvidia drivers they access that folder wich is what is causing all the problems.
so delete that folder. unfortunately that is much easier said then done. in the process of bundling all the xp information together vista managed to alter the file name of some files in there making them invalid file names and making it difficult for vista to delete them.
first you need to unhide system files, do this by going into control panel then folder options then view then clicking the bubble that says show hidden files and unchecking the box that says hid system files.
you can then go into windows.old and keep clicking through the folders untill you get right to the last folder and in there you will see two file, at least for me it was two files, that have really odd characters in their names. then using the delete invalide file utility you can browes your way to those files and delete them
MAKE SURE YOU ARE IN THE WINDOWS.OLD FOLDER AND NOT THE WINDOWS FOLDER SO BE CAREFUL
once you have deleted those files you can then go back out and delete the windows old folder normally.
now that windows.old is gone try to reinstall the latest drivers for your video card and see if the problem is gone.
someone that tries this please post your results with only trying this part of the fix so we can determine if this fixes the problem or if it is the second part since i made the mistake of not doing these two potential fixes seperately.
if that solves the problem great!
If not try this
get the program called powerstrip im using a free version of it. powerstrip is a powerfull display control panel it lets you do all sorts of things but all i had to do was really simple.
you may have to do this through safemode with networking.
once you install powerstrip it will ask you if this is your adapters default settings, say yes, this will lock your adapter to whatever settings are currently working, and since they are working now they will work when you reboot into normal mode. (if you are in safe mode if you are not in safe mode it means you are using a resolution that works)
reboot into normal mode
powerstrip will start up automatically on boot. check to see that your monitor is being correctly identified.
if it is then find the option in power strip that will allow you to ask it to detect the adapters default settings again. once you have that option open, right click on your desktop select personalize and set your display at the resolution you want to use. click apply then ok
go back to powerstrip and have it redetect the adapters default settings save them.
restart your computer.
powerstrip will start up with your computer and have your proper resolution, display, all set correctly, it will give you more control then nvidias control panel so if nvidia drivers are the problem it wont matter what happens with them because powerstrip now controls your video card.
finally, ive found that i dont actually need to have powerstrip running anymore. i went into its options and set it so it would not start up with windows just to see what would happen, and everything still works.
the only thing i have not actually tested it with is a game cause i dont have any for my pc right now.
good luck everyone and post your results hopefully they are as happy as mine have been so far.