Solved Are these symptoms of a dying MoBo?

[klauskunkel]

1. USB keyboard: Accessing BIOS most of the time not possible from any USB port, because keyboard not powered during boot process (although USB boot support is enabled). However, there are times when I do have access. Randomly. Tried different keyboards, both USB and PS/2. Sometimes I get lucky, most of the times not (reminds me of my teenage years).
2. After start up into windows, my second hard drive (storage) is not recognized some times. It's not there. After rebooting it tends to graciously show up. Diagnostics says all my drives are healthy.

Is there anything else I could/should try?
Would like to do start-up repair, but my keyboard problem (1.) prevents me.

 

[Mellon Head]

It could also be a failing power supply, though a failing motherboard sounds more likely in this case.

Just to test though, do you have access to another power supply that you can put in for a day or two to try it out?

 

[mrjimphelps]

Try replacing the CMOS battery. A dead CMOS battery can cause your motherboard to appear to be dead or defective.

 

[Megahertz07]

On BIOS, is fast boot enabled?
Fast boot disable USB and other peripheral devices.

 

[klauskunkel]

Appreciate all your input, thanks a lot. I found a loose cable connection to a hard drive which solved some problems. The USB issue still remains, fast boot is not enabled... Will now try replacing the battery.

 

[klauskunkel]

It could also be a failing power supply, though a failing motherboard sounds more likely in this case.

Just to test though, do you have access to another power supply that you can put in for a day or two to try it out?

Kudos to Mellon Head, you hit the nail on the head. Turns out that pretty much everything around the MoBo was in bad shape, had to replace first the graphics card and a week later the power supply, and to top it of I found some bad sectors on the system drive...
Although the MoBo is not out of the woods just yet, since I still have the USB keyboard access BIOS issue. But I will open another thread for that puppy.