Can anyone tell me how to find out the computer was last turn on?

The story is this: I worked in a community centre, and we use to hire an IT
company to fix the computer. However since we got them for the cheapest price
for the job. They have not been the best. There is a computer running WinME,
and few days ago, the IT company came and fixed the computer for some
reasons. We knew they used the ME machine. Just not, it doesn't want to boot
up at all. We have already elimate it is not hardware failure.

That's why I want to know how can I find out when is the last time the
computer was turned on. So we can prove to the company that it is their fault
and have them fix the problem.

I would highly appreciate for any help you give! Thank you!