OK, here goes
You could have several possible problems, I am on my 4th fan and 3rd pump! There are three things possible on the mechanical side, 1 actuator, 2 pump, 3 fan motor. Any of them could go bad. It is a big PITA to repair it. It may be impossible without the skill, tools and knowledge to do it. Check for leaks, it is a simple system, actuator releases the fluid to turn the fan, pump provides compression. BUT I've read many a tale about not being about to remove the connecting system bolts. Me for one could never get them apart. Search for an electric replacement fan. There are plenty of ideas on this site. check out the other post on actuator replacement.