MacBook Pro does not boot

I started to have some issues lately with my MBP 15" MID 2009 UNIBODY. It started to freeze on unexpected moments. When I for example tried to open a new tab in Chrome or just tried to close an application, the complete OS (latest Mavericks version) froze. When I try to do a hard reboot it gets stuck on the spinner.

Summary:

- MacBook Pro 15" mid 2009 unibody

- 8 GB (non original RAM but has been working fine)

- Latest version of Mavericks installed, has been working fine for some time now

- Superdrive not working but don't really need it anymore

This is what I already tried:

- Reboot: gets stuck on gear and fans go crazy

- Reboot in safe mode: gets stuck on gear / progress bar and fans

- Reboot single user + fsck check: gives me message "The volume Macintosh HD could not be verified completely."

Anybody can tell me what's wrong? I am happy to replace any parts if needed. Thanks in advance!