My 1986 300E will not start. When I put the key in 2nd position I can hear the starter buzzing but when I try to to start the car does not. I tried to jump start the starter by X27 and the solenoid and for each the fuel pump turns on but not the car(the starter just keeps buzzing). What do you think my problem is?

Check your battery voltage for a start.

Should be around 13 volts.

If it's not try swapping the battery, or jump starting the car.

If thats fine, then it could be the starter solinoid that is stuck. The contacts can weld together.

I'd remove the starter and bench test it.

Its a pita to get it out (I just changed mine this month) but this way you can test it.