There are several reasons your computer could be so slow. None of them are good. There are more possible causes than what I list here, but the top one's are probably:
1. Some idiot there decided to give your computer a "tuneup" and messed things up.
2. They did the wrong procedure on your computer because they got it mixed up with someone else's
3. Some dishonest shops will take your original good hard drive and replace it with a failing hard drive. They copy all the information EXACTLY as it was. With a pair of USB 3.0 docks, it can be done in less than 2 hours. I should know I do it all the time (the procedure itself, NOT stealing client's good hard drives). It's called mirroring. The bad dying hard drive read/write speed is usually significantly less than a good working drive and can cause severe slowness.
4. Your computer could have been mistreated while in the shop. A small amount of physical shock is enough to damage most hard drives. Check it with this utility:
http://crystalmark.info/software/CrystalDi...fo/index-e.htmlIt's the simplest and most user-friendly technician level hard drive diagnostic tool available.
In the future it's best to do the following before taking your computer in for service:
1. Make sure to shop around for a REPUTABLE shop. Check reviews on Google, Yelp, YellowPages.com, etc.
2. Write down the specs on your computer. Be sure to include processor speed and type (i.e. AMD A10-6800K 4.4Ghz APU), amount of RAM, and hard drive size.
3. Open up your computer and visually inspect each component. Write down serial numbers on the hard drive and look at the brands of your hard drive and RAM. Take a picture as evidence in case they try swapping parts on you.
4. Write the specs of your computer on a sticky note along with your name and contact information and put it on your computer. It acts as a deterrent to would-be thieves if they know that YOU know what your specs are. It also keeps your contact info right on the computer just in case they lose your contact information.