Hi,
The lagging issue maybe caused by overheating and a hardware issue. Here are some steps that may help in solving the issue.
- First load the laptop in Safe Mode and see if the same problem will persist because if it's not start doing a virus/malware cleanup.
- Here's a link for tools and guides:
http/www.tomsguide.com/faq/id-1691891/removing-malware-proven-completely-remove-bitcoin-mining-malware.html
- Once done with the cleanup and it's still lagging you'll need to open the laptop and clean the fans and make sure there's no dust and apply a new thermal paste onto both the CPU and GPU.
- If these will not work do load the laptop in BIOS and see if it will lag or freeze because if it does the problem would be a hardware (Motherboard).
- Also do try and run a complete factory reset just to be sure.