You seem tro have several issues.
First off. Find a freinds computer and download the McAfee removal tool. Load it onto your machine and fully remove all traces of McAfee.
Second activate windows defender as your only AV and firewall.
Third back up all of your data from this PC to extenal or cloud storage.Also if you have installed software find the discs and the installation keys.
Fourth go online and do a clean install of windows using the online tools. Before you do this make sure the copy of windows on your PC is activated with a key linked to your MS account or find your original installation key and have that to hand. Look at the pinned post at the top of the thread for instructions about a clean install of windows.
Your PC does not really have enough RAM and enough processing power. You should consider an upgrade. Don't try to rush the online install process it'll take a long time on your machine, maybe many hours.