Hi Gavinbremner,
I've processed your minidumps. Two minidumps crash with bugcheck code FE , 1 miniump with bugcheck 50 and 1 minidump with bugcheck 0A at timer interrupt routine. The culprit is related to faulty memory. Probably it is faulty ram or L2 cache memroy cpu.
You can run memtest to stress the ram. If memtest reports the ram is faulty, ram is bad. However Memtest is not a perfect tool to test the memory as some faulty ram can pass memtest.
Suggestion
1. Check the temperature of the CPU and make sure that it is not overheat (ie temperature < 60C)
Make sure that the CPU fan works properly
2. Reseat the memory stick to another memory slot
3. Downclock the ram
4. Clean the dust inside the computer case
5. Make sure that the ram is compatible to the motherboard
6. Check the bios setting about memory timing and make sure that it is on
7. Downclock the CPU
If it still crashes, diagnostic which memory stick is faulty
Take out one memory stick. If windows does not crash, the removed memory stick is faulty.
Debug report of Mini100505-06.dmp
BugCheck 1000000A, {f61, 1c, 0, 804e1637}
Probably caused by : ntkrnlmp.exe ( nt!KiUnlinkThread+7 )