Malware is usually the cause of this, so scan for malware first, see my post in this link
If it is clean of malware or you removed malware follow this procedure next.
Perform the following steps and update the computer:
Click Start, type Notepad in the Start Search box, and then click Notepad in the Programs list.
Copy the following text, and then paste the text into Notepad:
sc config wuauserv start= auto
sc config bits start= auto
sc config DcomLaunch start= auto
net stop wuauserv
net start wuauserv
net stop bits
net start bits
net start DcomLaunch
Click File, click Save As, and then type Repair.bat.
- In the Save as type box, click All Files (*.*).
- In the Save in box, click Desktop, and then click Save.
- On the File menu, click Exit.
- Right click the Repair.bat file that you saved in step 5, and then click Run as administrator. This action starts the required services. If you are prompted for an administrator password or confirmation, type the password, or click Continue.
- Try to install the updates again. If you can install the updates, delete the Repair.bat file. To delete the Repair.bat file, right-click Repair.bat, click Delete, and then click Yes.
Try enabling the firewall after these steps.
Source of Information