What's your OS?
Una muna, you have to back-up your files. But since, hindi nakakapasok ng maayos sa Windows OS mo, Ubuntu is useful for this. You can DL and burn Ubuntu in a CD, then boot from CD. Even without installing the OS, you can run it so that you can at least access your files, save it in a flash drive of external hard drive.
Then you can reformat your laptop and install a fresh OS.
Ps. As much as possible, partition your harddrive. Save files and documents in the partition and not in the system folder (lalo na huwag sa desktop). Always back-up your files. Magloko man ng tuluyan ang laptop mo, at least, hindi mo iiyakan ang files mo.
Good luck!