DIMENSION E520 compatible cpus

Hi everybody, I've been trying to find out exactly which cpu's are compatible with this dimension e520  model as I want to upgrade, but I 've been having trouble with it.

(Pentium D 2.80Ghz currently installed)

For instance, the dell website says these are compatible:

Intel® Pentium® 4 
Intel® Pentium® D 
Intel® Core™ 2 Duo

<ADMIN NOTE: Broken link has been removed from this post by Dell>

But today, I tried a Intel® Core™ 2 Duo E7500 , and it did n't work, ie fans turned on but no post (cpu is fine took back to shop they tested it then i re-installed old cpu)

I know that some people have installed e6600 & q6600 & q6700 cpus but now they are quite old and more expensive.

Please,

does anyone know, or know where, I can find a complete list of compatible cpus for this machine?

Help!

:)