Bios Mods -The Best BIOS Update and Modification Source

This BIOS (version 5.23) bypasses the CPU white list check for the HP Pavilion slimline c3750t. It allows you to run up to core 2 quad Wolfdales

Another mod from DeathBringer, allows you to run 771 Xeons on the 775 irvine board (s3500t in my case)

Make/Model: Foxconn mcp73s01/HP Irvine GL6E/HP s3500t/Pavilion Slimline
BIOS Version: 5.23

Here is mine running an E5450. Not sure if it supports any higher TDP's than 95w but I had a Core2 Quad Q9400 in it before and it was stable.

I sees a strange thing on your screenshot - the maximum multiplier is x8.5 instead of x9...
Try to do Loads Defaults in BIOS.