Windows Defender won't turn on, receive error codes 0x800705b4, 0x8050800d and 0x80070426

After my computer crashed (able to move the mouse, but not change windows or open task manager), I restarted it and checked my security settings, only to find that Windows Defender had turned itself off. On opening Windows Defender, I get the error code 0x8050800d

with the message "Some history items could not be displayed. Please wait a few minutes and try again. If that doesn't work, clear the history and try again". I have waited quite some time, tried restarting the computer, and searched the help files (no article

on the problem was present), and I can't see a way to clear the history from the Windows Defender menus.

When I try to turn the real-time protection on, I get the message "Windows Defender couldn't turn on real-time protection. This operation returned because the timeout period expired" and the error code 0x800705b4. According to the bottom of the Windows

Defender window, it did a scan about the time that my computer crashed.

I tried what was suggested in the Windows 7 forums (I know that Windows Defender is very different between Windows 7 and 8), starting the Services program, and it says that Windows Defender Service is running, and has an automatic trigger start. I tried

restarting the program from there, but to no avail.

I do not have any other virus scanners or security software installed, and have only installed windows just over a week ago.

Thank you in advance!

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