I cannot open any files, devices, or paths on my PC

I have no idea how this could have happened it just wouldn't let me access anything on my PC and I try'd to fix it but couldn't find any valid solutions on the internet or from looking around. Please help the message that pops up is "Windows cannot access the specified device, path, or file. You may not have the appropriate permissions to access the item." I am the only user on my computer and it's an Acer aspire with windows 7. Please if you have any ideas of how to fix it I would appreciate it allot thanks.