92 SVX woes...

[Rolling92SVX]

Some times when i go out to my SVX to start it i hit the key all the lights come on and nothing happens.. i hit the key 2 or 3 more times then it starts....why?
it dose not click like the battery is dead and the security alarm is not on.
also i have a slight clunking and vibratio in the rear the previous owner told me i need to changes the rear diff. mounts how hard is this todo and where can i get them at?
also at 50-80 there is a small vibration in the wheel all tiers/wheels are balanced and it don't need a front end alignment because when i let go of the wheel the car still goes straight even during vibration