MP 1,1-5,1 Early 2008 Mac Pro won’t remain on

[joevt]

I’ve upgraded it with Kingston Ram totally 68gb (8 x 8gb).

Did you mean 64 GB?

Unfortunately while I’m fairly technologically savvy I can’t say I know what maxmem is or how to know if I have it. I can remove some of the RAM if necessary would 32gb be more appropriate?

nvram boot-args to view the current value of boot-args.
sudo nvram "boot-args=maxmem=63488" to set maxmem to 62 GB since macOS runs slow with 64 GB. I wonder if setting maxmem higher than the amount installed is ok?

 

[KeesMacPro]

@Ashleekhb

If you look at my posts you'll see a link to download The Technician Guide for Mac Pro 2008.
This can be very helpful especially for troubleshooting, maintenance, etc.etc.

 

[Ashleekhb]

I wonder if it’s still good. It’s one possible cause (but by no means the only possibility).

A cheap Radeon HD5xxx or 6xxx will do, I guess.
I have 1 Radeon HD6670 (PC card, not Mac) which works fine in my MP1,1.
I bought another GTX680 (PC card, flashed with Mac compatible BIOS rom), also works fine.

More cards are described in this thread. MP 3,1 can take almost any not-so-new PC VGA cards.

If you are the nostagic type who prefer Mac VGA card, 2nd hand GT120 or HD5770 are available as well.

I decided to give the RAM another try and in a strange turn of events I got the computer to turn on. Only one of the two sticks is being read by the computer (no error lights though) but the computer is on and running well.

 

[Nguyen Duc Hieu]

I decided to give the RAM another try and in a strange turn of events I got the computer to turn on. Only one of the two sticks is being read by the computer (no error lights though) but the computer is on and running well.

Glad to hear.
Now with the confirmed working RAM sticks and working RAM slots.
Try to move it to other RAM slots to verify if the slots are bad.
If all the slots are good, then test each RAM stick to detect the bad ones.

It takes time, but eventually, you'll know what to do next.