Alt tab + black screen + no vga signal

I bought my computer half year ago, and it was fine, but after changing the monitor, whenever i enter a non-windowed mode game, it will randomly black screen and the rate is pretty high...

and when I start the game, I alt-tab back to window mode, it black screen again...

while black screen, i can still hear the game's music and so i am sure the game is running... since my heroes are dead when i can see them...

I end up pressing the monitor on & off button to tried to get it back to normal, after a few times, like around 10++, i finally manage to see vga input signal = active ...

the previous work just fine, which bought in half year ago too...

monitor: hp widescreen crystal bright 19", HPw1907
Core 2 Quad Q6700 2.67Ghz
2Gb ram
nvidia 8500 GT
vista home premium 32bit

Please... in need of help really...

some additional information...

I just format my computer and it doesn't fix the problem, its my first time format and re-install a window vista OS, so i am not sure if it is CLEAN in FORMAT, i didn delete the partition, juz format it.

I am not sure for 1 thing, the new monitor should be fine at the beginning, after i install a program remover and I remove a nvidia phantom driver... accidentally hit it... does it affect ?

Please help, I hope I didn make things more confuse then it is...

1.- When you reformat your computer and installed a fresh Vista, did you also install the CD that came with your Computer? you know, the one that brings all the drivers for the mobo, network, etc, etc?

2.- Do you know for a fact that all of your drivers are up to date? I don't mean from the CD but latest from manufacturer?

What I would do is go to the Mfg of your board (specifically for your Audio & Network, not so much for your Bios if you feel that you're not capable of updating this one), video card & Monitor and get the latest drivers, download them to a folder you'll recognize later and install them... it should solve your issue for the most part.

Just remember, to install fresh video drivers, you must uninstall the ones you have now, DO NOT install the new ones on top of the ones you already have.

I think I had solved it... should be that program remover which remove my phantom driver...

I reformat again, this time i delete all the partitions and create a new one...

It solved... next time i won't simply delete drivers...