Most of these problems are just dirt in the floppy, connections for cables, chips etc.
Older they get, more grimy they get.
Hard drives are sealed, but motors can need a little time to adjust if off for a while. Sometimes tere's a humidity sensor on the circuit board, keeps it off until it's warmed up and dried off a little bit.
Capacitors are usually pretty good for 20 years, can last longer. Depends how the machine has been run, and how corroded they get.
When electricals, electronics, mechanicals etc get dirtier, they not only corrode more, they heat up more. Speeds up the whole ageing process.
