If you are looking for a temporary fix, you can try sfc.exe /scannow:
After that download Malwarebytes Anti-Malware and AVG Antivirus (free version) and let both scan your entire drives.
Based on what you describe above, I would assume your computer is heavily infected. Although you could try removing them, you have essentially allowed trojans to corrupt your entire computer. If you keep using it at this point and you are not sure you have removed all trojans sensitive data may be stolen from you including banking information and so on.
I therefore recommend to buy a new hard drive and remove the current hard drive before you install it. Copy some important files from your old hard drive onto a USB stick AFTER scanning them carefully. Make sure that the new and old hard drive are never connected at the same time.
Set up a completely fresh PC and read everything you can find about firewalls and security software. This is a good start:
Windows Essentials is not sufficient to secure a PC.