You need a kit for the cartridge slot, don't try anything else or you'll f*ck it up. For the cartridges use windex or rubbing alchohol and just roll up a paper towel so you can scrub them real good.
Alcohol is fine for cleaning metal contacts,windex is not. Windex has chemicals that speed up oxidization in metals,thus ruining them. Windex will also cause oxidization in the plastics used to make cds and dvds and laser disc,so its not recomended to use it on those either.
As for the system:
Take a toothbrush you dont need. Drench it in alcohol,and scrub the cart slot contacts out with it,and then blow it out with a air can,then do it all over again.
Eventually it shoudl start working fine.
If not,and you want to do a tad more extreme process,take the system apart,if you have the required bit,and place the pcb in the dish washer,if your waters not too hard. It will get it very clean. Youll have to set up a oscliating fan aimed at it for around a day to let it dry,every now and then hitting it with a blast of air from a air dryer helps too.
I do this with arcade pcbs,and MVS systems and it works pretty much every time.