Lenovo Thinkcentre Edge72 (3493) only powers up when case open

Thinkcentre Edge72 (3493) PC only powers up when case open - if PC started when case open cover can be put back on and PC continues to run, but will not subsequently restart if PC turned off unless case opened.  There is no obvious physical damage to cables etc.  Onset of problem was sudden, no warning.  Annoyingly machine out of warranty.

Any thoughts on what this might be?

Many thanks
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Chief AvocadoChief of Problem Avocado'sCommented:
Disconnect the chassis switch? Normally a white square button at the rear of the machine which is visible when the case is open.   This would not fully explain the issue but might get you going again with the lid on.
mnewmanaAuthor Commented:
Well I can't find one and no reference to one in the hardware manual.  I rather assume the problem is a "case open detection microswitch" but can't find one
Jan KlimaCommented:
Check if the SATA hard drive is connected properly and SATA power cord does not have a contact with chassis.
mnewmanaAuthor Commented:
Weirdly the problem went away after I cleared the motherboard CMOS.  The rational is that I was wondering if the s/w that detects an open case was confused but I was not hopeful.

'Course may just be a coincidence and it was a dodgy connection but I really couldn't see any physical damage!

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mnewmanaAuthor Commented:
Think my explanation is reasonably full
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