Intel PII won't boot

[joglon]

A couple months ago, I got a PC-CHIPS mb (M726v33) from a friend. Last week I changed my Celeron433 with a PII 450 from a collague, cause his mb only supported fsb 66. Last WE I bought a PII350 (secondhand), for the M726.
Prob is, the M726 don't want to boot with the PII350. My guess is has to do something with the PII350 since the psu, mb, bios, testram of 16Mb SDRAM and PCI videocard worked well with both the Cel as well with the PII450 (thus with fsb of 66 as well as 100).
I'm puzzled cause when I check a ISA slot and the bios chip with a digi-probe, signals on the adress and data bus are pulsing which has to mean that the proc is functioning. Can it be some timing prob on the proc (faulty resist or capa), or could the proc be stuck between some adresses and doing a loop of always the same instructions from bios?

[Comage]

Hi there! Welcome to SysOpt!

Did you set the motherboard jumpers to reflect the correct CPU multiplier?

[joglon]

Wel Comage, firstly greetings to you too, and every other member of the Forum.
Yes, I even double checked the settings, every-time with the different processor. I even tried to underclock the processor (by which he had to run even much more reliable). For the 450 it worked fine too (on both mb's), but the 350 didn't give a glimp.I didn't tried it on my main system, for the simple reason, not to blow it up.
I didn't mentioned this in my previous post: the 350 don't always 'boot'. Sometimes it kept stuck after 3 or four pulses, and sometimes it continues to give pulses on adress and data bus, but no real boot (screen remains dark, no ticks of mem check and no beep).