i have a flashing folder with a question mark. I've tryed to do this my self but it's not working.

It generally means it can't find the operating system on the selected boot drive. If it remains flashing ? for over a minute, then that partition needs to either have its directory fixed, or the hard drive needs replacing or the connector for the hard drive needs fixing.

Is your data backed up from it? If not, you will want to take it in for a data recovery first before doing anything.