1 monitor stopped be detected

My PC is dual boot - Windows 7 32 or 64 bit. I have 6 Dell monitors connected to my PC. I usually boot into win 7 32 bit where all 6 monitors work. Today I booted into Win 7 64 bit and one of the monitors does not show the green power light just orange. The other five are OK. If I restart and boot into win 7 32 all is well again and the monitor with the orange light in win 7 64 bit goes green. In win 7 64 bit there only shows 5 monitors. Any idea what might be wrong? I assume that it is a software problem.

I would start to investigate settings in your video control panel. What kind of GPU do you have? How are these six monitors even connected?

I have 2 x Radeon HD7700 + GTX 1070Ti
3 monitors (DELL E190S) are connected to the GTX 1070Ti via Startech 3 way splitter DP port on the GTX in – 3 x DP out to VGA monitors.
1 monitor (DELL P190S) is connected to the GTX via dual-link DVI port to dual-link DVI port on the monitor

1 each (DELL P190S) are connected to the HD7700's dual-link DVI port to the dual-link DVI port on the monitors. It is one of these monitors that is not working in the win 7 64 bit. It does work in the win 7 32 bit with no changes in any lead or other connections.

This setup has worked flawlessly for at least 2 years.

- - - Updated - - -

Hello F22 Simpilot
Thank you for helping me.
here are some screen shots
The image Win 7 32 and 64 bit.jpg is identical on both systems
The image windows 7 32 bit screen resolution.jpg Shows all 6 monitors detected and OK
The image windows 7 64 bit screen resolution.jpg shows only 5 monitors
The image windows 7 64 bit screen resolution press detect.jpg after pressing the detect button. clicking the No display detected drop down box only shows Try in VGA mode. This too does not work.

I have a felling you need to use the AMD GPU driver control panel for the configuration of those connected monitors and the Nvidea control panel for the configuration of its connected monitors.

Mixing two different brands of GPUs is not a good idea...

I too are believing that it is something with the Radeon HD7700 graphics card but this system has worked setup has worked flawlessly for at least 2 years. I will look in to this. Thank you again

Well, it's kinda like plugging a hole on a steam pipe with bubble gum. At first it may work for awhile, but eventually it won't....