Only when it crashes, sometimes get a computation error

Example? If possible, provide a link to the stderr of the result.

Yes with BSOD?, usually point to hardware issues.

What do they say? Examples?

Mini-dumps...LOADS...

Can you zip some of them up and provide them through a Skydrive or https://www.transferbigfiles.com/ ??

Heat? - NO. I'll apply additional cooling

Meaning what? You didn't have that yet and are now doing it, or you were already doing that?
When you check with something like Core Temp, what's the maximum temperature the cores get, when idle and when under load?

Updated Bios, tried several versions of Boinc, now trying the newly released 7.1.1

Unless you are an alpha tester, do not use development versions. They will be buggy and give additional reason to crashing. Only test development versions on a stable system. The whole 7.1 range will be development versions. Part of the 7.2 range will also be development versions. Just do not use them.

And then it's not BOINC that causes the crashes, but the science applications, as these do the calculations that cause the stress on the CPU/GPU, and thus the heat, memory use and all I/O operations. So just stick with one BOINC, which for the moment is 7.0.64, the latest recommended one.

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Also a long time user (since 1999). I want to use BOINC for the science, not as a test to destruction of my PC. I have Win 8 Pro (don't ask) on a HP Pavilion G6 with an AMD A6-4400M APU and Radeon HD7670M graphics. Symptoms are that after a bit (pretty random it seems to me) BOINC consumes all my computer resources, despite my preferences having been drastically lowered to try and combat this. I was running pogs, Einstein and SETI - trusted SETI the most so stopped the other two, but the fault still happens when just SETI is running. Result is I cannot use the mouse or the keyboard. The only solution is to hold down the power off button for a hard shutdown. If I hibernate my laptop it continues until it powers down due to excess heat (which I find out about next time I boot up).

I also used BOINC on my desktop until the NVidia graphics card died. I'm wondering now if it didn't die because of being over-stressed by BOINC at 100% use?

Although this is an older thread I'd like to make an addition to it.

A few weeks ago I suddenly had lockups on my Win7 PC. The first few times it happened while I was away from the keyboard and upon returning the screen was blank (no video output from the computer) and the monitor kept looking for a digital or analog signal.
A bit later I saw that the cursor began to "stutter" and moments later it would not move at all. A hard reset was all I could do. I was thinking about the last things that changed and suspected a program that recently was updated.
Since no one else reported problems on their forum I kept digging further, lowering boinc CPU use in % and number of threads. It looked better but still there were lockups, some even after 30 minutes after a restart. Workunits that failed were always Einstein never one of the other projects. After suspending the Einstein workunits I had no more problems.
The computer ran 24/7 for days until I re-activated Einstein and after a few hours again the PC grinded to a halt.
I deleted all Einstein WU's and suspended the project and so far no more problems.
Something in the Einstein WU must not like my setup. At least it's solved (for now). I'm back at 100% CPU :-)

I have had the same problem starting a couple of weeks ago. I disabled the Einstein project and it disappears. The PC is high spec with no previous issues. Checked the Einstein message boards and no mention of such issues.

I see no mention of your problem on the Einstein Boards, what app was this with? you could have been running a multitude of different apps,

Looking for users called arfurdent at Einstein only shows one, also from the UK, neither of his PC's are particularly high spec, both only being Core 2 Duos, both with very low spec GPUs:

Computers belonging to arfurdent

Claggy