Cursor stuck in top left corner
when I start up the mac the cursor is stuck in the top left corner and won't move.
Only clicks with one finger still work.
I found out by accident, that sometimes the trackpad works just fine when the WiFi router is turned off (just a coincidence?) Then, the trackpad works very precisely and all gestures function properly, but only until the mac is put into sleep or is shut down, then it is just like before.
I assume, that this is a software problem, because when it works, it works perfectly.
For now I am using a tethered mouse.
Here is what I tried so far:
- Reset SMC
- Reset PRAM
- Reinstalled el capitan several times, I always erased the SSD completely
- set all other devices (like smartphones or other notebooks) to flight mode, since I was told that sometimes bluetooth signals might interfere in some way with the mac
The warranty period run out a few weeks ago, that's why I'd like to avoid a costly repair.
Thanks a lot in advance :)