Windows 7: Computer suddenly slow and starts up with non-changeable classic theme

The computer was perfectly fine yesterday; normal speed and using the default Windows 7 aero theme (save the background obviously).

Since today the computer is suddenly slow from the start-up already; When it comes to the "configuring windows" screen it takes about a minute instead of the second to get to the login screen. Then when I log in, everything is in the classic theme. A warning also pop-ups during start-up.

Here's a screenshot where you see the task bar in classic theme while it should be aero theme. You also see there the warning on start-up. It basically says it can't connect with a Windows server, namely the System Event Notification Service.
http://i50.tinypic.com/2a8nfyc.jpg

After start-up other problems are occurring.
First of all, parts of the computer has become slow. The most notable is right-clicking on the desktop (and only the desktop!), it will take ages before the right-click menu is loaded.
Secondly, I can not change the theme, was my initial thought to do. All themes except the classic themes are greyed out and not selectable.
Thirdly, the antivirus, Avira Antivir, starts up disabled, and whatever I try, I can not enable it. This started to happen after a few start-ups.



So yeah, quite bothersome problems. I have tried the following solutions:
- Scan my computer with Avira. I've scanned every single file my computer has, but my computer didn't find any viruses. This scan was done before Avira started acting weird.
- System recovery. I first send it back to yesterday, which was right before an Windows update. The computer was fixed after the system recovery, but after a reboot every problem was back. Now for some reason none of the system recovery points are working, including the first one I tried.

So far I have one possible conclusion: It's the Windows update from yesterday. It installed only one update, which was a definition for Windows Defender, KB915597 definition 1.129.1102.0 to be precise. It's also the only difference between today and yesterday, and before and after the first system recovery. Sadly this update re-installs itself immediately after a system recovery, and I can't find anything about this update on google, so I can't say for sure this is the cause.

Anyone knows how and why this happens and how to fix this?

Try booting up into Safe Mode and downloading, installing, and running a FULL scan with Malwarebytes: Download Malwarebytes Anti-Malware 1.61 - FileHippo.com

Just finished scanning with Malwarebytes in safe mode, and it found a virus (a trojan.dropper?) in a .exe of a program that should be safe. It probably got infected somehow.

Anyway, the computer seems to be working fine now, so thanks for that. However, Avira is still acting weird. It still starts up disabled, and whatever I do, it doesn't want to enable. When I open Avira it says that two services aren't working properly:
http://i46.tinypic.com/23t051v.jpg

When I click on "fix problems" it will run the updater, which won't do anything since it has the newest update already.

So yeah, anything for this last one?

Try reinstalling Avira.

Before reinstalling Avira remove it completely then download another antivirus program (Microsoft Security Essentials, Norton Antivirus, etc.) and run one of them. The reason being if a virus got though Avira then there is a chance it still will. Good Luck.

But I already scanned the computer with Malwarebytes and found the virus, I surely don't need to install a different antivirus just to scan my computer again?

Anyway, I reinstalled Avira, and it works properly now. Everything seems fine now, so I consider this solved for now.

That's why we did a Malwarebytes scan I don't want to start changing up their setup a bunch if we have everything working. Every antivirus has it's weak points and every one of them will let atleast 1 virus through. I worked on a computer that had Norton on it and Malwarebytes found infected objects. After cleaning that system up and removing Norton, then system got so, so much faster. i recommend Microsoft Security Essentials, but I've heard good things about Avira.

Okay, it turns out the problem is more or less unsolved.

The computer started up with the original described problems again, except Avira kept working fine this time (which might have been the virus, so lucky catch). So I immediately started up in safe mode and scanned with Malwarebytes again. It found nothing.
So I started it up normal and to my surprise it worked normal again. I did a few reboots as tests, where all worked fine. Then I discovered something; I unplugged my headphone when I started Malwarebytes. So I plugged my headphone in (in front side of the computer, not directly in motherboard) and started it up; the problems reoccurred again, so the problem is my headphone. Well, half of it.

I remembered that the day before this started, I plugged in the audio cables of my Wii component cables in my line-in port (backside of the computer, directly in the motherboard). So I did some tests with these cables and the headphone, and got to the conclusion that the problem occurs when both these cables are plugged in. When one or none of them are plugged in everything goes fine. This is only for the start-up, after that I can plug them both in without any problems.

Now the obvious solution is to either unplug one of them before start-up or plug the component cables in my monitor again (and thus get bad sound). But I obviously want to have them both plugged in and start up without any problems.
It might be also worth to note that I've set the line-in port to direct the sound to my headphone. Else I wouldn't hear the sound going in the line-in, so maybe that could be something to do with this?

So yeah, any ideas for why this happens and how to solve this?

I have the same issue except its when I plug in my Microsoft Lifecam, just started last night when I installed it, I've never had any issues like this before so I would be interested to hear the solution to this as well

Ok, I take that back, Its from my line in from my xbox...