My MacBook Air's screen goes blank every time I switch the laptop on and does not allow me to access my files. HELP!

Hello there,

My MacBook Air has been acting up lately. The screen goes blank every time I switch the laptop on and enter my password. I can access my System Preferences whenever from the top bar makes an appearance. Safari somehow opens up a blank page too, strangely enough.

Trouble is, I can't access my other files whatsoever - not the dowloads and documents. Not even my apps. I've been contemplating reinstalling my OS. However, system has been warning me that my startup disk is almost full but I cannot access my files in order to make more space.

Please, help!

Many thanks in advance,

Ely