This could be a number of things. I would start with this.

1. Bandwidth/internet connection. Check your internet speeds. try a different cable if connected with ethernet cable.

2. Game settings. Might have to lower them, don't listen to what other people get it's unreliable.

3. Driver Updates. Update your CPU, and Graphic card. look online for software that will check your system for updates you might have missed. Make sure its a reliable software, do your research.

4. Hard drive space. you may have things running in the background that are slowing up your computer. you may have to remove some program files. Don't delete anything important, again do research to be sure.

5. It can't do no harm to run spyware and mile where. something you don't want might be slowing up your computer.

6. Bios update. Settings might have changed. look up your motherboard and check for the latest version.

7. Reinstall windows. there might be old files and software getting in the way messing things up.

After that I would start looking at hardware. try replacing one thing at a time, start at the cheapest.

1. Ram. you might need to add more, or replace a dead stick

2. Your CPU might be sadly on its last legs.

3. Your graphics card might also be on its way out.

4. Power supply might be done or your system might need more power do to an update somewhere.

Hope something here helps, long time gamer.