Sounds like the memory cap was probably not the problem but the act of working on board (connectors, etc) may have been the problem.
Make sure the case of the oscillator isn't touching one of the traces on the top of the board. It should be raised up a hair.
Get some alcohol and a soft bristle brush - clean up some of the flux on the top and bottom of board and then recheck solder joints.
The 100uF cap is old but not the source of your problems.
Before you do any more mods to that board - easiest to get a logic probe and go from there.
With logic probe & voltage meter, you want to divide and conquer - figure out where the problem is: power, clock or reset.
Very first thing to do is verify you have good power at the CPU board. Measure for 5V directly across that 100uF cap, C1. How close to 5V does it measure?
With logic probe, see if the clock divider is running or not. Can be checked at Z2, pin 9.
If pin 9 has no activity then the oscillator isn't running, check Z3, Pin 6.
If the clock is running then I would double check the board for the reset modifications you made.
Next with logic probe, see what your reset is at the CPU, U1 pin 40. Catching the actual reset pulse is unlikely with just a probe.
The quick tests above will tell you if it is a power problem, reset problem or clock problem.