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I didn't try plugging the PSU directly into the wall but did try on another 4 way extension (this one not surge protected) and didn't get any different result, I can try directly into the wall though if that can make a difference.
The chap who built my machine originally and then again after the first failure thought it might be a shorting problem but can't understand why it is happening after it has been working for a week and not straight away. I will test the PSU again before it is rebuilt and maybe some spacers for the screws into the motherboard could solve the issue.
The h440 comes with spaces pre placed.
If it just a week after you paid someone to build it I would take it back and let him find the fault. I would argue it down to his work and he should at least find the fault for free.