SATA connector is the physical cable that attaches inside your computer from motherboard to the back of the hard drive.  Also refered to as ribbon cables.

The cable ends at a connector, one end goes into the motherboard slot and the other connector goes into the hard drive.  sometimes these connectors that are on the cable don't fit in tight to the hard drive or the motherboard connector and can be half seated (partially connected).

Also you should check your computers BIOS settings and make sure you computer BIOS is seeing the correct settings and everything is enabled.

putting in a hard drive is not just simply putting in a hard drive and going to town.  you have to play with BIOS settings and make sure that Windows in loading the proper drivers for the hard drives.

common problems are BIOS settings incorrect.  comuter works but you get really slow performance cause the hard drives and BIOS is not setup correctly.  the settings are written on the top of the hard drive case and these are the settings that sometimes have to be manually input.  newer motherboards will automatically recognize new hard drives but it's always hit or miss depending on how old or new your hard ware is and BIOS versions etc.

another problem is Windows may not have proper drivers in your Windows Device settings and your running your newly installed hard drives with the wrong driver.  this can be solved by going into windows control panel and run the application install new hardware, Windows sometimes will pickup the correct driver that way.

I don't know how techno savy you are but there are a lot of things that can cause slow down on a system.

if you just copied your Windows operating system directories and did not do a new install then you will have tons of issues with speed etc.

another things is when you put in the new hard drives you may have inadvertanly unseated a card, other cables etc.  you should open the computer and just push gently on all your connections and make sure everything is seated correctly.  I used to have a card in my computer that any time I opened the case the card would pop out half way and my computer would just crawl until I went back in a reseated the card.  ground yourself before toching anything in your computer.  static kills electronics and it only takes a tiny bit to fry parts.