System Failure, need some advice on replacement parts

Hi all

I built my main home / home work system coming on three years ago when the Conroe chips first came out, buying the cheapest part and o/c'ing. This has served me well for the intervening time, replacing the graphics card earlier this year from a 7600GT to a 9800GT for GTAIV, but the system has now died (will not post) and having swapped virtually everything out, reset cmos etc I can only conclude that the board or CPU has failed. So...

APPROXIMATE PURCHASE DATE: Now.
BUDGET RANGE: £0-£500 (The £0 likely only applicable if anyone wants to gift me some old parts as they upgrade to i7 )

SYSTEM USAGE FROM MOST TO LEAST IMPORTANT: Linux work machine 40 hrs a week (mostly web / shell related), Windows gaming system in evenings / weekends.

PARTS NOT REQUIRED: All from the failed system, Screen, Antec P150 quiet case, keyboard, mouse, speakers, OS. DVD drive, hard drives. I have a PSU I wish to reuse a Nesteq 450W and 2x 1GB sticks of corsair value select 667 ddr2 which can be reused if they fit the new system but I'm happy to pension off if not. I'll also be reusing the graphics card a Sparkle 9800GT as it was only purchased earlier this year.

PREFERRED WEBSITE(S) FOR PARTS: Any of the reputable UK web retailers, quite happy with a pre assembled / pre oc'ed bundle as it would save me time assembling I just haven't got spare at the mo.

PARTS PREFERENCES: None specifically, the case is a little tight however from memory, so port placement on the mobo could be relevant if not a deal breaker.

OVERCLOCKING: Yes, better bang for buck and all that.

SLI OR CROSSFIRE: Maybe, never used up to now and PSU prob wouldn't stretch to it but preference for SLI mobo rather than crossfire just in case as prefer Nvidia cards for their Linux drivers. That said, previous mobo was crossfire

MONITOR RESOLUTION: Currently 1280x1024. Would like to upgrade to 22-24" at some point but the cost of this build will prob put that back some months.

ADDITIONAL COMMENTS: The machine this will replace / rebuild was chosen to be as quiet as possible without water cooling, hence the choice of PSU and Case that I'll be reusing. I also used a ninja scythe heatsink before and this served well, I presume I can't reuse this as from memory the mounting kit had an x shaped bit of metal that stuck to the base of the motherboard to strengthen things, I'm quite happy to be corrected on this however In all honesty I do wonder if it's weight contributed to the death of the board...

The only other requirement not mentioned above is that the motherboard has a hardware raid chip for a disk mirror. By that I mean one where the array appears as a single disk transparently to the OS without additional drivers being required on install of the OS, the ASUS P5WDH deluxe I'm replacing here satisfied this with it's "ezbackup" or similarly oddly named function.

Having had a quick search around, I've more or less ruled out an i7 system as it seems to be a cost premium for not much gaming advantage although it would likely fit in to my max spend. I don't do any video encoding or rendering for work so the benefits also wouldn't be seen there. I'm leaning towards a quad core intel chip purely because I'd like it to last ideally again for a few years and whilst there is no current advantage with a quad over a dual in games it seems sensible to have the extra cores for when the games that use these arrive in a year or so, I believe this should come in around £250 - £300? Do please feel free to correct me however.

Many thanks in advance for your advice.