LGA 775 Xeon mod, slow system

[majaczos22]

Hi,
I just replaced my good old E8200 with Xeon E5440 and things didn't go as planned. I updated the BIOS with 067A microcodes, swapped the CPU (I purchased the one with mods already installed), BIOS booted up normally, altough is shows old CPU clocks (2.66GHz instead of 2.83GHz), Windows booted up fairly quickly as well.
Things went south since then. It's slow and laggy as hell, more like a sideshow. CPU usage hoovers around 50% on all four cores. Most processes have no user attached to them.
Now I'm stuck. Any tips, ideas? Thanks.

Edit. Can any of those be a problem?
https://i.imgur.com/pp4WN9U.jpg

 

[majaczos22]

Edit2: Windiws started nicely just once. Shutting the system down and starting again takes forever and it still didn't finish.

System starts normally in safe mode. Altough functionality is extremely limited, most drivers don't work, I cannot open CoreTemp, CPU-Z displays such error:
https://i.imgur.com/UD6Kfai.jpg

So it seems like my OS (XP) and driver can't handle new processor? Or there's something wrong with CPU itself?
Is there a chance to change/update all drivers in safe mode? Or do I have two options: new OS or revert back to E8200?

 

[majaczos22]

I got advised to disable Intel C-STATE in the BIOS and it worked like a charm! Everything booted normally, works fine (except high temps but Ineed to work with them a little longer).