I seen that. Amazing shape and really nice buy, but shipping cost is too high for me.
A vacuum will never not turn on unless it is not getting power to begin with. It might buzz or hum or just immediately blow, but it will never just not do anything. If the cord had a short in it, it would explode the cord or blow the breaker at the short, so that rules that out.
The only other thing is the contacts in the switch could be dirty or bent out of true, not hard to do since the toggle switch is in a bad spot prone to damage. I have a 45 year old Leviton light switch at my front door, and the switch that powers the light is worn out from so many decades of on/off flipping, and I have to jiggle the switch or hit the wall with my fist to get the light to turn on after I flip the switch and the light fails to turn on.
Dismantle the switch and clean up or put the prongs back into place and should be good.
There's Celebrity II switches on eBay, which although not original, would suit just fine for testing or replacement if need be.
https://www.ebay.com/itm/Hoover-Cel...819690?hash=item4216c4862a:g:kFQAAOSwR2RaB3IL
Notice for the Celebrity II they changed the switch to a rocker style and not a protruding toggle switch, so I bet this was a common fault with this vacuum.