Games : I can't open my minecraft PC worlds

I can't log in to ANY of my Minecraft worlds. I have some modded ones for 1.7.10, but I can't log in to vanilla worlds either! I can log on to servers, but not singleplayer worlds. The worlds are in the saves folder and in singleplayer, but I can't click them to delete or rename etc... The mods I have are: Galacticraft Core, Galacticraft Planets, NotEnough Items, MicdoodleCore, CodeChickenCore, Thaumcraft 4.2 and Witchery. I do have Forge installed for 1.7.10, but it still won't work. I think there is something wrong with Minecraft's code, because it even won't let me log on to FTB worlds! I am using Windows 8.1, and I can't bring up the menu or click the start button on the left bottom side of my screen, so I have to press the Windows key on my keyboard. Please help me. I tried restarting my computer and it fixed! Though I need to know what the problem is and how I can prevent it next time.