How to test whether Biostar TB250-BTC in operational?

I bought second-hand TB250-BTC but it looks like dead:

  • no led blinking

  • cpu fan not spinning

  • no action when I try to turn it on (with/out DVI, with/out M2, with 24-ATX connector)

  • changed CMOS battery did not help

How can I test whether it is operational?

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