Does the machine show any sign of power or does it look completely dead, and not respond when you press any buttons?
Which power switch are you referring to, the one on the control panel?
This sounds like a lose connection, between the control panel and the treadmill.
There shouldnt be any other fuses inside the unit, I am unable to get hold of a service or instruction manual for your model as its obsolete, however I would start off by checking any obvious cables which you can see comming from the control panel, they normally come up the stem of the unit and hidden by a small removable plate on the back of the control panel.as you have confirmed
If you have the manual to hand it may be worth following the setup instructions to see if that tells you where the plugs go and then double check the pluggs are properly connected.
Please let me know how you get on.
Just wanted to check in and see how your getting on?
Unfortunately as I cant find a service manual and the unit model is not a known brand I cant offer any further guidance, so will opt out in hope another engineer can assist who has repaired\serviced a similar unit before.