Need help isolating display problem to solve this mystery

The PC is an HP p6710f, Athlon II x4 640, 12 gigs of DDR 3, motherboard is a Foxconn 2AB1. Windows 7 is the OS. The monitor is an I-INC 28" display. When I woke the PC from it's sleep mode today the monitor displayed only a dark gray. After a few minutes the display gradually became brighter until it was all a very light gray. Since the monitor was lit from edge to edge I assumed it might be a graphics card problem. I uninstalled the MSI R7 240 with 2 gigs of ddr3 in the bay and installed a Sapphire HD 7750 I had on hand. The 7750 has 1 gig of ddr5. I booted the computer back up and had the same gray display with no graphics whatsoever. Thinking the monitor must be the problem, I went over to use my laptop to browse for new monitor. After a few minutes I happened to look over at the desktop monitor and was surprised to see my Windows 7 desktop screen being displayed. I'm mystified as to what happened to cause the problem and when I can expect it to happen again. In the meantime I've set power options to never power down the computer and monitor. If anyone has an idea about what may cause a problem like this I'd greatly appreciate your technical knowledge to solve it.

Connect the monitor to other PC or laptop. If the problem persists , it's the monitor to have issues.

I tried the monitor on a laptop. No problems. On my Hp p6710f display will randomly display vertical lines over complete screen. Sometimes display is complete orange. Computer will reboot on it's own. The last time it happened it did display a blue screen.

It was:

Stop: 0x00000116 (0x FFFFFA800c1490101, 0xFFFFF8800504B714, 0x0000000000000000, 0x000000000000002)

atimpag.sys - address FFFFF880504B714, base at FFFFF8800503B000,
Datest amp 5ce54911

Any solutions?

Uninstall graphic card drivers and install it again - see the last version of the driver on the producer site.

Thanks, but I completely uninstalled the driver and installed the newest non-beta driver, but the problem remained. I'm baffled.

You might want to try setting Hardware Acceleration to None and see if that isolates the problem. Hardware acceleration can be set via the Display Adaptor Troubleshooter in Display Settings.

I went into the control panel and then display, but there was no place to disable hardware acceleration and the troubleshooter is greyed out and can't be accessed. Since my previous reply to a post I used the AMD cleanup utility in Safe mode. I went from an R7 240 to an HD 7750. No matter what I do the Device Manager, Windows System Information and the detailed program SIW list the R7 240 as the Current graphics., but of course the card installed is the HD 7750. I can't understand why. Suddenly without rhyme or reason the display turns white and the computer reboots. I can usually troubleshoot problems fairly well, but I can't even get the computer to recognize what card is installed. By the way, even ATI's software which is supposed to automatically scan for the graphics adaptor lists it as R7 200 series. Any answers?