Resolved Desktop powers on briefly and shuts off

Friends Win 10 refurbished Lenovo ThinkCentre desktop tower model MT-M7373-CTO serial number MJ04489. Wasn't turning on all the time. Then stopped completely. Tapping near front on off switch caused it to come on. Thought the switch was bad and tried to get a new one. New ones are different look to the old one. Cut switch off and tapped bare wires together to get it to turn on. Goes on and then off but then won't come on at all. Did the paperclip green/black wire test on power supply plug and the fan comes on. Changed the cmos battery and fan came on briefly but then quickly stopped. Thoughts?

 

Just had it sitting here plugged in and all of a sudden both fans came on for 10 seconds and shut off.

 

'refurbished' may be your big problem. I would suspect the PSU is faulty.
I have ever only had to replace 1 (one) start switch in nearly 20 years of tinkering with comps.
The fact it only fired up the fan and then randomly flicks on and off - I would change the PSU first.
The worst scenario would be the motherboard.

 

I've bought many used or refurbished comp over the years for folks who couldn't afford new. Guess I also have never had a switch go bad, or a PSU yet either. Suppose $100 to another used unit is better than $30-80 towards a PSU, which could fix problem, or maybe not?

 

The other option is to get the PSU tested. I've built quite a few comps and used 2nd hand parts just for the experience and I invested in a simple PSU tester which didn't break the bank.
https://www.amazon.com/Insten-24-pin-Power-Supply-Tester/dp/B005CTCD6S
Similar to this unit.

 

I think I'll get one of those. Didn't realize they were so cheap. Think we'll get a different comp for this person and I'll test the other one later and keep as back up. Thanks!

 

Note those testers are not conclusive but much better than nothing - or guessing. I keep this one in my tool bag for house calls. I like it because it has an actual read out of the voltages and I can then tell if they are within tolerance or not, instead of just present.

Acceptable ±5% Tolerances:

12VDC ±5% = 11.4 to 12.6VDC
5VDC ±5% = 4.75 to 5.25VDC
3.3VDC ±5% = 3.14 to 3.47VDC​

They are not conclusive because they only provide a small (typically 10Ω) load instead of providing a full range of expected loads. Plus they don't measure ripple and other anomalies that affect computer stability. To conclusively test a PSU, it takes an oscilloscope or power supply analyzer - sophisticated (and expensive!) electronic test equipment requiring special training to operate, and a basic knowledge of electronics theory to understand the results.

Since most of us don't have those laying around, swapping in a known good PSU is the next best thing. Short of a spare PSU, these testers will certainly tell you if a voltage is missing, which sounds like the problem here.