Black screen and sound flutter crash

Hi, recently when I play any game it'll load for a bit(30sec-2minutes) then my screen flickers and turns black then I can only restart. Before I would receive the message "signal out of range" "Horizontal frequency is out of range." "vertical frequency is out of range." with a number xhz, But now no error message, just flicker to black screen, and monitor display light turns to that of standby mode and the sound flutters in the background, seems to work fine at desktop/internet/etc..

Stuff I've tried:

At first I've been running my games at 1024x768 at 75hz, true color 32-bit, then 2 years later(now)I started getting the error. I changed it down to 70hz at 16-bit which seemed to work (for 2 months) but I started to get them again. I've tried 1024x768 16,32 bit at 60hz,70hz,75hz,85hz with no luck.

I tried to update my monitor drivers but the company doesn't have them for my model.
I tried running the game in 800x600 but it still crashes.
ran the game in full size/ window size, still crashes.
tried different driver versions 5.9-6.11 ati drivers, no luck

specs:
envision eft720 monitor crt
ati saphire 9800pro 128mb, running with drivers 5.9

any help greatly appreciated, thanks

What Hz is your CRT