Facebook account is not opening

Hello,
my facebook account is not opening since two weeks.it says that i had installed some software due to which it is not opening..but i do not remember installing any software recently.here is what it shows when i open my facebook account,

It looks like you downloaded software that is affecting your Facebook account and showing you unauthorized ads. It's common for people to be tricked into running programs that offer features that aren't available on Facebook, such as adding custom themes or seeing who has viewed your profile.

What is Adware?

This software will show you spammy ads that aren't approved by Facebook. They can also introduce security vulnerabilities, slow down your computer, and clutter up your news feed with ads so that you end up missing content from your friends.

If you would rather continue using this software, you may stop this process by clicking on "Log Out" in the upper right hand corner. Note that you won't be able to use Facebook from the computer where this software is installed.

please help me in overcoming this problem

thankyou.