See if you can find an online manual for your specific model to see what processors it supports. If it came with a 1.6ghz cpu, it's probably too old to support a faster bus speed. The 400mhz bus processors were available up to 2.8ghz.

I did some CPU tests which was the fastest and easiest thing to do.

originally fitted with a Pentium 4 1.6 / 256/400

i have tested:

P4 1.8/256/400 and start correctly at 1.8Ghz
P4 2.66/512/533 and start at 2.66 (means 133mhz bus supported?) but crash after 2 minutes
P4 3.0/512/800 and start at 1.5ghz (means not support for 200mhz bus and why start at 100mhz bus instead of 133?)

any consideration will be welcome tnks

Can't you find a CPU support list for your motherboard?

I have an old SiS-based Gigabyte board with unofficial 533MHz bus support. Gigabyte added "O.C." in parentheses next to each 533FSB processor on the CPU support list. It will attempt to run 533FSB CPUs at full speed (automatically even, which is kind of a ballsy move on Gigabyte's part), but it's far from stable. Run any system intensive program at 533FSB and it'll eventually reboot. I guess it could also be down to aging components; perhaps it ran faster CPUs more reliably when it was a younger mobo.

Anyway, it sounds like you have a similar kind of system!