You can download .iso copies of the bootable diag CD at various levels as far back as 5.1 to see what it will boot from here:

https://www14.software.ibm.com/webap...load/home.html

As there is no LED display on your machine it will be hard to spot where the problem might be.

I think 5.1 will be your limit.

Does the CD light flicker when booting from CD?
Can you boot other media to check the CD drive and boot list selection are working properly?