Try using Disk Utility to do a Disk Repair, as shown in this link, while booted up on your install disk for OS 10.6.8 and under. If you are running 10.7 or 10.8 run Disk Repair from Disk Utility on your Recovery System. It shows you how in the link.
You could have some directory corruption. Let us know what errors Disk Repair reports and if DU was able to repair them. This could just be a start in repairs and you may need a better utility to finish the job.
Then Repair Permissions.
No need to report any Permissions errors........we all get them.
Oh....and we need to know this...
Can you tell us how much RAM (Memory) you have? It's listed by clicking on the in your title bar....go to About This Mac and it's in the 1st window.
We would also like to know what size hard drive you have and how much free space is on it.
If you click on your Hard drive icon (should be upper right hand corner of your screen)...when the window opens it says at the bottom how much Free Space you have on your drive.
If you go to the , click on About This Mac, click on More Info... in that window. The next window says how big your hard drive is under Hardware....click on Serial-ATA.....look under Capacity:
We need to know this cause if a hard drive is too full it slows things down and creates operational difficulties.
Replace the hdd with SSD? how much RAM does it have? what model year?
I don't know but is there a forum for the Mini? I see this identical question with notebooks also, we here are a forum for tower - 4-6 hard drives, 32-96GB RAM, expansion slots, and you don't here about slow.
I looked at a Mini, but they are using slower i5s than what you can buy for $220 on Amazon. I wonder but doubt but use to be the processor was even something that could be upgraded. And with RAM prices and such easy to build a small PC with more options (even logicboards now with Thunderbolt).