Not sure if this should be in Overclocking forum really so apologies if its wrong. I'm concerned. I spent several weeks tweaking my system and finally settled for what I believed to be a worthy but relatively conservative overclock and have been using it for several weeks with no issues at all. Good benchmarks, low temps, no crashes, rock solid. I havent made any tweaks or updates to it for many days and powered off last night as normal. This morning the machine wouldnt boot! Just hung on the POST screen and after several attempts I had to reset BIOS by removing battery and got into setup and reverted all CPU and memory timings to stock. This enabled me to boot into Windows but applications would randomly stop responding and the 1 totally reproducable error that I could make happen was trying to start 3DMark06. It will hang every time on the loading screen and lock the whole machine up in the process. Once it bluscreened and I briefly saw in the error message "MEMORY CONTROLLER" before it rebooted (I've since unticked the "automatically reboot" option in advanced system properties so will have more chance to read it if it bluescreens again).

My system specs are as follows
Asus P5N-E SLI (added a heatsink to SB and 2x40mm fans to NB) BIOS 0505
E6600 2.4Ghz (was running at 3.24Ghz) It's an Akasa cooler which I guess is stock as I didn't put the system together originally it's from MESH.
2x1GB OCZ PC28500 1066Mhz (the SLI ready stuff) in the black slots
BFG Geforce 8800GTS OC
Creative Gamer Fatality Pro Soundcard
2 x 500GB 16MB Cache 7200.10 Seagate SATAII Drives on SATA 1 and 3 (non-RAID)
550W HEC PSU

I've never managed to get the OCZ RAM totally stable at its rated speed of 1066Mhz but realise this board is fussy on RAM and so had settled for running it at 960MHz at 5-5-5-15 and it had been rock solid. The NB voltage had been manually set to 1.563V to get this stable with Mem voltage at 2.2V. I today updated BIOS to the new Beta0604 to see if it helped at all but it hasn't made any difference to my problem..or anything else for that matter.

Now that problems have started I've even tried taking the OCZ memory out and putting the old stuff back in that came with the machine (Elixir PC2 5300) and running it at its rated 267 (533) speed at 4-4-4-12. Nothing helps. I can still use the machine and even play a game, (something I would have expected to make it fall over straight away), but random problems occur with Windows apps and 3DMark ALWAYS locks the system up now...it never did before and reinstalling it hasnt made any difference. My biggest fear is that continued use of the machine may randomly corrupt my data.

I'm coming to the conclusion that the NorthBridge has suffered permanent and irrepairable damage from being overclocked? Does this sound likely after just a month or so? Can anyone help me at all??? I dont want to replace the motherboard only to find its not that. I'm confident its not the RAM (both sets Ive tried pass Memtest86 and its highly unlikely that the old stuff that Ive now put back in would have had any problems). I suppose it could be the CPU itself?

This is my first stab at overclocking and after patting myself on the back only last night at a job well done I'm now wishing I never started in the first place!!! Its like some unknown force saw me congratulate myself and thought, "smug git...this'll teach him"!!!

Is there any diagnostic tool that will specifically highlight problems with the NB or CPU?

And does anyone know how Memtest can pass if the Memory controller is faulty?? Surely if the controller is dodgy then there should be problems with the test even if the DIMMS are OK???

Confused... any help appreciated. Thanks.