Blue Desk Light keeps blinking

The flashing green light on your Behringer Pmp500 mixer desk indicates that it's receiving a signal, but it's unclear why the first 4 channels aren't working. Make sure that all cables and connections are properly secured and that the power supply is adequate for the mixer's needs. If the issue persists, you may need to consult a professional for further troubleshooting or repair.

THE pC IS DEAD OR IS In sleep mode (flashing LED means that)
so start post why is my PC dead and tell what PC it is makers name an model.
hint: desktops PC has 6 sides one of them has service tag label and tells what PC this is.
Q1, PC FANS MUST SPIN DO THEY? IF NOTHOLD POWER BUTTON ON PC , DEPRESSED FOR 10 SECONDS AND RELEASE.

Sounds as though you have a backlight issue. How old is the monitor?
The keyhole with the lock sign is for a security lock to lock the monitor to a desk so it cannot be stolen.

Please check the pins at both ends of the VGA cable.

How old is this thing? Mine is about 4 or 5 years old... junk it!

bad capacitors inside the monitor they need to be replaced, or if the power light is blinking then there are transistors that need replacement

You need to make sure that the mouse is near the receiver, or that the reciever didn't fall down or got moved too far away from the PC/desk or the mouse itself. Furthermore, check to make sure that the batteries you inserted were new or fully charged batteries.

There are many laptop desk lamps available that will give you the light you need. The 1405 does not come with an illuminated keyboard.