emosun wrote:

After some googling I found that it's possible that a 3 long beep on an ibm machine can mean a keyboard error. However the keybo […]
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After some googling I found that it's possible that a 3 long beep on an ibm machine can mean a keyboard error. However the keyboard is plugged in.

I've already tried:

Different cpu and ram combinations
Setting the cmos and recovery jumpers differently.
Making sure the cpu jumper were correct.
Opening and closing the chassis switch connector
Dummy fans plugged into board.

Have you tried plugging in another keyboard? 😜

For this kind of problems I use a POST Diagnose card.

https://en.wikipedia.org/wiki/POST_card

You could get on of those on some unknown selling sites for about 10-20 bugs. It displays a 2 digit number which you can lookup in a booklet to identify the problem. So you know were to look.

There wouldn't be anything to plug the post card into , this board doesn't have pci or isa slots.

I haven't tried another keyboard because..... well I only have one ps2 keyboard , and I can't imagine the machine wouldn't post simply because there wasn't a keyboard plugged in. But the keyboard works fine on all my other older machines.

Ah, didn't know that there weren't any PCI-ISA slots. There are also COM cards available for Laptops and so. 😁

I also never had a machine that won't boot because of no keyboard, they mostly give an keyboard error message. But did you tried to boot without keyboard?

Yes I tried it without a kb as well.

Something I just noticed is it beeps the exact same even with no ram installed. I've tried every sd ram stick I own which is A LOT. But I did notice this ram requirement in the manual.

Chapter 2. System Board Features
System Memory
Three dual inline memory module (DIMM) connectors are provided on the system board. The DIMM
connectors are powered by
+
3.3 volts. This voltage allows for low-power operation and supports 64-Mbit
technology. Each DIMM connector is a 168-pin, gold-lead socket. For the pin assignments, see “System
Memory Connectors” on page 34.

The system board supports:

A maximum of 384 MB of memory in the PC 300XL; a maximum of 512 MB in the IntelliStation M Pro
Dynamic random access memory (DRAM) only
64-bit extended data out (EDO) nonparity (NP) and 72-bit EDO error correcting code (ECC) memory
modules

Any configuration of DIMMs is acceptable. However, DIMMs must have the following characteristics:

Must be 168-pin, unbuffered,
+
3 V type
Must have gold-lead tabs
Must have 60 nanosecond (ns) access speeds only
Must have a height of no more than 3.05 cm (1.2 in.)

Also, note the following:

EDO NP modules and EDO ECC modules can be mixed, but they will configure as NP.
To enable ECC, all installed memory must be of the EDO ECC type.
Note:
Single inline memory modules (SIMMs) are not supported in the PC 300XL and
IntelliStation M Pro.

So, the mainboard came without ram? Could be the wrong type of memory. Same problem like the PowerMac 4400 and only whit the 4400, with some special type of memory.