Mac mini now incredibly slow...???

I'm trying to figure out why my Mac mini is now incredibly slow. It started a while back. Back in the day, I used to wipe it clean and do a new install with my system disks but now with online system software upgrades..., not sure what to do. My last actual system disks are probably OS 10.7

Specs:
Mac mini (Early 2009)
Processor: 2,26 GHz Intel Core 2 Duo
Memory: 4 GB 1067 MHz DDR3
OS version: 10.11.5 (15F34)

I've attached a screen shot of my activity monitor. Any ideas or suggestions would be appreciated.

Thanks.

Marc P.

Attached Images

Screen Shot 2016-07-10 at 08.21.25.jpg (124.9 KB)

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