I recently built a new system with the E8400 chip on a P5KE mobo.  I was getting hi temps under load.  I checked the HSF to see if it was properly seated but it was slightly crooked.  I straightened it and now the temp is stuck at 26c and does not change.  The HSF does not seem to get very warm under load so I think it is properly installed and have gotten about 15% jump in 3dmark score.  Any ideas?

hmm, maybe i'm having the same problem ... mine seems to be seated fine but at stock speeds i'm getting 57c with 72c loads, temps read 59c in bios and less under ntunes monitor .... seeing as tho your getting 26c and i'm using the xigmatik cooler ... something's wrong on my end ...

 
 
If your 3dmark scores went up in the processor section after you reseated your heastsink then I would say your processor was getting hot and the processors was issueing stop_clk to keep it from reaching a thermal setpoint.  The performance increase can be attributed that you processor stopped throttling itself.

Before I reseat the HSF, the CPU temp readings were working.  Any idea why it is now stuck at 26C.  My system temp works and usually gets to about 32-34C under load.

Mmmmm, your sentence contradicts itself.  You say it now stuck at 26C but temps get to 32-34C under Load.  Are you reading these temps from within Bios or using program to correctly derive the processor Temperature?

Take it back to the shop and exchange it.
 

Update your bios and see the stuff where other users have fixed the problem.
 
If that doesn't fix the problem then take the cpu back and ask for an exchange.
 
Or get a Q6600 which actually works and is a better all round cpu.

My E8400 with stock Intel cooler idles at 34-35C and reaches max 47C at load with 1.1k rpm fan speed. I keep Probe II open at all times.
 
@Reynod: the Q6600 is NOT a better CPU mate. It depends on your needs really. If you are a gamer like myself and not do anything else cpu-intensive (having word processor or IE open is not such) then the E8400 is way better than the q6600. But if u have a few tasks runing at the same time that are CPU intensive, then the Q6600 is for you.

True ... but at least that cpu seems to work properly ... is cheap, a good overclocker, and all round 4 cores gives the pc a longer likely life.
 
The op didn't state what he uses it for.
 
I am a gamer ... you are ... he didn't say.
 

I was thinking about taking it back, but the store doesn't have any in stock and the 30 day return period is up tomorrow.  Everything else works great.  I'm getting 12500 in 3dmark06. no overclocking.  I may take the CPU back out and reseat it and the HSF and see what happens.  I've been using Coretemp and PC wizard to check temps.  They both also show 26C processor temp with core 1 at 37C and core 2 at 44C and each never change.

Seems odd that you were getting high temps, and then played with the HSF and are now getting a locked reading......

It looks like the minimum temp reading is 26C.  I changed the Qfan setting to so that the CPU fan runs slower until the temp goes up to a certain point.  I loaded the CPU with the fan at 1100rpm and it went up to 40C.  I guess it was just running below 26C with the fan running at 2000rpm.

So from this I surmise that it is working really well and you have a nice and  cool running cpu.
 
If your going to go and overclock it I suggest you read some of the other threads .. .specifically on Wolfies ... and don't try pushing any where near the voltage that others have put into the Conroe cpu's.
 
Do your research first and see what others have used safely first.
 
I am sure it you ask others will assist ... there are at least a dozen users here with experience in that regard.
 
Good luck.