Whenever I try to open My Computer (safe mode or not, apart from the last time I opened it), the window opens but is non-responsive. It will be blank for about an hour, then show the drives, devices and such but if I click on anything it's non-responsive for another hour. during this time there is 50-68% CPU usage whether any other application is open or not. I've done a scan using Malware Bytes and Microsoft Security Essentials (which are out by 5 days, but that leads to my next point) & neither can find anything.
I have also had problems installing and uninstalling things since I got the laptop (present from my mother when she bought a new one, it's 7-8 years old). This mostly stopped when I installed Mareware Bytes in safe mode and ran a scan, which found a trojan, adware and a lot of other stuff. I also had to re-install Windows Installer. I still have a lot of trouble installing updates.
The computer takes about 6 minutes to boot up. I have uninstalled non-important progams that I don't use or need. I opened My Computer while typing this and it opened up fine. Disk Defragmenter doesn't work.
What could be the Problem?