SQL Server 2008 R2 Express with management tools installation failure
I found the cause of the problem. Recently I'd set my default program files folder to my hdd, because my C: is a 60 GB SSD. The key is located in the register at HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion. The keys "ProgramFilesDir" and "ProgramFilesDir (x86)" are the ones that need to be default ("C:\Program Files" and "C:\Program Files (x86)") in order for it to work. Sorry for the unnecessary post.