Size of Taskbar

My taskbar doubled in size for no apparent reason and now my only options are twice as thick as normal or invisible. How do I get it back to its normal size and why did it do this? I've tried everything (at least I think I have) and am very confused.

 

Does your taskbar have the quick launch bar on one level and your open programs on the other level. Have a look at the picture I've attached to see what I mean. If so, put your cursor just to the left of the program button (in my picture it says "Size of Taskbar - Win..." on it). You want the cursor between that button and the seperator line to the left of it. Then, click and hold the left mouse button and drag it straight up to the top line. The program buttons should then jump to the top line and you should then be able to resize your taskbar.

Of course, you need to first make sure the taskbar is unlocked before doing this. Right click on the taskbar and uncheck lock the taskbar.