It will be difficult to tell if these events are related, as there could be a lot going on with your system, but I can give you some basic pointers that will help out.

1. I recommend to reinstall windows every 1-2 years, it's amazing how much faster your system will feel 

2. Update graphics drivers

3. Open task manager and check out your startup tasks (one of the tabs) - you may have programs starting on boot that you never use

4. In a similar vein, go to windows Programs and Features in settings and uninstall programs you don't need/use

5. Without WoW running, look at task manager processes and filter by CPU and memory and see if there is anything with heavy usage.

6. Installing WoW on a separate SSD (or hard drive, but SSD is much better) from your operating system drive will give you better loading times and maybe a small performance bump if you are currently on an old HDD

It probably ran better just from the restart. How often do you restart your PC?

WoW started running better after malware scan, now it doesn't, tech support help?