Computers can start slowing down over a few months to years. This can be a lot of factors like. Windows Corruptions or Hardware needing upgrade.

Try reloading computer and running tests ,check your Task manager/Performance to see if some of your Hardware needs to be upgraded.

Usually upgrading Ram and HDD To a new SSD will solve the issue, but if CPU is running at 100% then the CPU is the issue and needs to be replaced.

Find out how to speed up your computer here.