Well it happened again today whilst my son was playing counterstrike source, the screen froze, the mouse and keyboard became unresponsive and the sound seemed to be in a recurring loop.

I am starting to think it's an overheat problem on the CPU, is there any way I can check?

download CoreTemp to monitor your CPU temps

Download GPU-z to monitor your Graphics card temps.

Make sure you have all the latest video and sound drivers installed.

I ran both coretemp and gpuz programs,

coretemp: at idle was 38-43 degrees between all 4 cores, rising to 51 -48 when running counterstrike source for an hour.

gpuz:  gpu temperature was 64 degrees at idle upto 74 degrees under counterstrike source. fan speed @ 25% throughout 1550 speed

gpu seems a bit warm at idle to me, though im not an expert on gpus lol

anything there to suggest a problem with either cpu or gpu?

There is nothing wrong with your CPU temps. Those idle temps are right on target. Mine runs just a tad bit cooler at idle. The 420 doesn't have the same cooler as my 720 so your in use temps do come in a bit higher but well well within the safe limits. I would not worry one bit about your CPU temps

You GPU temps are again right on the normal line for idle and gaming. If you want you could pick up Riviatuner to setup your gpu fan to run at higher speeds when gaming but 74 under load is well within most other reported temps. Heck there are others whose idle temps start in the 70's.

So looking at the CPU/GPU temps they are not something that would jump out and point to your issue. 

I'm still having the same problem, PC totally locks up, screen image freezes, sound goes into recurring loop, mouse and keyboard unresponsive.

I've ran diagnostics and scans, all results showing PC as fine.

So, how do i escalate this through to customer support when there's nothing showing as faulty hardware wise or corrupt software wise?

As it is, it can wait, gonna be away from home for next 4-5 days, but suggestions would be most welcome :)

Sorry no advice but you are not alone. Keeps freezing up. Thought it was SP1 but don't have that down loaded on this again after I reformated to Dell factory. I am begining to think this was a major lemon of a machine.

Back from my break feeling much refreshed :)

Cubbienan I can understand how much it must be peeing you off, it is with me.

I've not had any problems like this until the gfx card was replaced, but I dont think it's a gfx card issue, I could be wrong though.

I think the next thing will be to progress this further within Dell and see what comes, tbh, I've got a reasonably good games machine that wont let me play games, it's not what I signed on the line for, even more so when it originally did.

How I explain this one to tech support is going to be interesting to say the least.... No faults on diagnostics, no driver problems, no other faults, no logs it seems about PC freezing up.... cant wait!!!

Well, I downloaded the CPU monitor and all four cores are under 40. I also downloaded the driver from nvidia for the geforce 8800gt this weekend and (knock on wood) it has not froze. Sure as I write this, it will freeze. I have not reinstalled the sp1 and afraid to do so.

We will wait to see. I even played on my laptop outside yesterday and it didn't loose any connection which it does constantly. It was the first time I had 5 bars on the network too. Could it maybe work for once?  I should send Dell my bill for all the hours I have spent trying to make these machines operate like they are supposed to.  LOL:smileyvery-happy:  In my dreams!

Well it's still happening, all firmware and drivers are up to date, and it still happens only when playing games, I think it's time to call Dell and request a new gfx card to replace the refurb they sent me when my original new card died, since this problem only started after receiving the refurb. :(

Well, since I posted this, the machine hasn't froze up but then after the reformat it did the same thing for a while. I am still hesitent about sp1 though.

I've not been on the PC for a little while due to a short holiday and work commitments, tonight, thought I'd chill out while she watched some soaps and loaded up Counterstrike Source, 40 mins into the game and once again, I get screenfreeze and the sound stuck in a loop, only way to cure it is to reboot the PC.

I'm getting a bit tired of this, to be honest, I expected better from Dell, will ring them as soon as I have a few hours spare, because no doubt it's going to take that long to get to a tech who might have an idea of what the problem might be :(

it is still freezing up but I keep restoring it to where it didn't. Really getting tired of it. but what can you do. They will just make me reformat to Dell Specs again.

I am also having XPS laptop connection to internet through a router. Don't know if it is the router or the 420 being a "brat". I thought I fixed it but then the 420 froze and restored then lost what made the M1520 not loose connection. Wonder if I did the right thing by ordering two XPS systems.

Problem fixed with the insertion of a new 8800GT card 2 days after ringing technical support :)