As it starts being confusing and/or hard to find solutions for your issues we are making a thread where you will find every solutions found that have solved others' issues.
Please bear in mind that these solutions are not all official and might not work for you.
If you have tried every solutions posted below, please create a thread (if this hasn't been done yet) with your DxDiag and as much information as possible.
Another thing that will help us help you is to make one thread per person and per issue. If you see another thread that looks like your issue, please do not post in it. Even though issues may seem very similar, they might have different causes.
You will find the solutions here: (or just scroll down to the appropriate part)
If you have found a solution which has worked for you, please send me a PM with the link to the post giving this solution, as I will be adding them as soon as possible.
I hope you will find a solution in this thread and if not, we will be helping you as soon as we can.
Disclaimer: Incorrectly modifying or disabling any process in msconfig or in any other core windows component might create a risk of crashing your system, and is to be attempted at your own risks.
Before making changes to a file (system or game file) please make a safe copy in another folder, in order to be able to reverse the process if necessary..
DISCLAIMER #2: Please be careful when downloading from external websites as these might contain virus/trojans. If you find a link to be related to a virus/trojan, please report it immediately so we can remove the link. Thank you for your understanding.
PLEASE READ THIS THREAD BEFORE POSTING YOUR ISSUE ON THE SUPPORT FORUMS.