Well, an ACF7P is inadequate if you are really pushing a Q9550.
I cannot push my Q9550 faster than 3.6 GHz while maintaining stability. It has what used to be a really good cooler, but my chip is a C3 stepping, not the E0 that tends to overclock better.
At around 3.6 GHz, you are reaching the limits of most chips.
If you haven't already, adjust your memory settings to give you a memory clock twice as fast as your FSB frequency and try running your memory at 2.2 volts if you are not already.
Your PSU, while not the best in the world, if working properly, will not be the limiting factor of your overclock.
Learn to use the BIOS. You have more control over the system that way.
btw my chip is a E0, So it should overclock well!
can you give the best settings for 4ghz pls ,because I failed many times LOL !
by the way i have pc2-6400(400mhz)2GBx2 and a 32 bit system,maybe thats the problem?