Windows installer Service is not correctly installed

I'm currently trying to clean up an old laptop that we had laying around the house for possibly school. It had been ages when I had initially powered it on. I'm not sure who the last person to use it was, but they did a number on it.

So upon first boot, when it finally came to the desktop screen the task bar flashed into sight, and then gone, as well as desktop icons. I got a prompt saying windows explorer was no longer working, and would try and fix it upon next restart. I was stuck in that loop for a while until i finally got to where I could make a new account, which worked.

Once I got into the account, I started running avast immediately, full system scan. It found roughly 20 viruses, and then wanted to perform a boot scan as well. I restarted and let it run through it's scan. Found another 20 or so.

In the end, here I am trying to uninstall unwanted programs to hopefully speed up the machine a little bit. When trying to uninstall in normal windows, it just comes up with a prompt saying that it will begin the uninstall shortly. So i thought it might work, but two days later it still said that. So i restarted in safe mode in hopes that I could do it that way. Now I am getting "The Windows Installer Service could not be accessed. This can occur if the Windows Installer is not correctly installed. Contact your support personnel for assistance." any time that I try to uninstall from safe mode.

Any help would be greatly appreciated

Update: I'm also noticing that any time I go to shutdown my machine a handful of popup webpages show up. I had noticed when running my first full scan with avast that it would give its popup notification saying that such and such was being blocked, and that would popup roughly 200x during the scan. and prior to me being able to scan it would do that too.