Compaq Computer not booting

Didn?t take notes so specs are general
Compaq 800Mhz AMD/ 100Mhz FBS, XP Home SP1, 40 gig 5400RPM H/D. 3 memory chips, different Mnf. and types -
Memory installation: Slot 1, orginal 64MB pc-100: Slot 2, 64MB pc-100 (4 chips): Slot 3, 128MB pc133 (16 chips). Memory chips have been installed and working for over a year per client.

Client messed around inside case resulting in no boot.
Removed all Memory chips, NIC and Modem card.
Attempted to boot with each chip individually, no joy.
Cleared CMOS (pulled battery for 5 min), system booted with both pc-100 individually. No boot using Pc-133 memory chip.

Installing pc-100 in memory slots 1 & 2 system failed to boot. System would boot from each memory slot using both known good chips individually or together in slots 1 and 3. Thinking incompatible memory I installed compatible memory chips from inventory in slots 1 and 2, no joy.

Not thinking I re-installed clients memory in slots 1 and 2, system booted. For giggle and grins added pc-133 to slot 3, system booted and Windows recognized installed memory at 262MB and was stable.

Re-install of modem prevented system from booting and was removed. This I believe was the root cause of system not booting.

Need some thoughts on memory issue, what I may have missed or caused this type of issue.

Bill