The USB ports connect through the internal USB bus (which sounds logical )
The keyboard and trackpad ALSO connect to that USB bus (internally)
AND, the bluetooth - also the built-in camera - all connect to the USB bus.
The interesting info is that your right-side USB port still works?
Be sure that there's no SD card in the slot (and that also uses the USB bus!)
So, you can see that the USB bus is has a lot of connections.
You can't reset that bus, unless the keyboard is working. The keyboard connects to that bus, so it's just another device that stopped working.
So, you need to reset the USB bus. Try this:
If you have one working USB port, plug a USB wired keyboard into that working USB port. Restart with a PRAM reset (holding Alt(option)-Command-P and R)
This should work from a Windows keyboard, if you don't have an Apple-layout keyboard to use. On a Windows keyboard, you would hold the Windows key-Alt-P and R.
You should get a startup boot chime. Keep holding the same 4 keys until you hear the boot chime two more times, then release the keys to let the system start normally.
Does your trackpad start working then?
If so, then you likely have a good reset - try the built-in keyboard and bluetooth.
Serendipity is a lucky guess !