Pictures in the computer library all look the same

IM sorry but I cant find an answer to this anywhere. In my computer which is Window7 Home I was having a problem with lag in games so I went to youtube and found some things that I can do to reduce lag. But now my desk top looks different and ALL my pics look the same. Attacked is a pic pf my pics. They use to look like small versions of my pictures. I want to undo what I did but I dont remember what I did. It involved going to the register and typing a D word and also something about "using best performance" (changing it I think) I am far from a Geek and have no idea what to do. Can some 1 help me get my pics back to normal? the desk top I dont care about that much.

I dont no how this pic will upload so:cry to describe it all the pics look like a mountain with clouds and water. After I click on the pic then I can see the real pic.:cry

 

As you have changed a registry setting and want to revert back you may be able to do so with System Restore. You need to choose a restore point that predates the changes you made, if you have such a restore point, and if that doesn't fix it you can reverse the changes that System Restore makes.

You can find System Restore on your Start menu under All Programs > Accessories > System Tools.

 

Go to Control Panel\All Control Panel Items\Performance Information and Tools
Click Adjust Visual Affects
Find Show Thumbnails Instead of Icons and make sure that's checked.

 

Thank you very much for your replies and a special thank you to cabbiinc

it was as simple as 1 2 3 and it worked!! ty sooooo much