XPS 8100 -No Power to Keyboard/Mouse & Monitor in Power Save Mode

My current setup is a Dell Desktop XPS 8100 with Windows 7. 

Over the past couple of months during normal use of the PC, the monitor would randomly phase out into power save mode for a few seconds and then come back & work normal.
On occasion the monitor would turn white, blue or white with black vertical stripes.  I would have to do a manual shutdown of the PC.  The system would restart and function normally.

Approximately 2 weeks ago the screen turned white & when I restarted the PC, the monitor was in power save mode, my keyboard & mouse would not work.  Neither the keyboard or mouse are receiving a signal or power as the led lights are not on.  The keyboard & mouse are both connected via USB ports.

*Replaced Power Supply Unit

   After install, the monitor was still in power save mode and my keyboard & mouse would not work.

*Replaced Motherboard

   After install, the monitor was still in power save mode and my keyboard & mouse would not work.

*Tested RAM (4 sticks) -Switched out sticks inbetween different slots.
*Reseated Battery
*Reset CMOS Jumper (COM 1)

After reseating the battery & resetting the CMOS Jumper, the sytem properly booted and I had power to my monitor, keyboard & mouse.  Approximately 5 minutes after bootup, the monitor went back into power save mode but I had power to my keyboard & mouse.  I did a manual restart of the PC.  Upon bootup, I once again had no power to any of my 3 peripherals.

I am completely at loss as to what is causing this to happen & what to try next.  Any suggestions would be greatly appreciated.