I have a laptop computer that I had when I was working at an IT company. I don´t work there anymore but I could keep the computer (Lenovo)

Suddenly my wireless internet didn´t work anymore showing error "insert SIM into the mobile broadband device" and month later connectiong to internet with cable got disabled

I don´t know the password to sign in as an administrator on domain and whatever I try to do/install/change settings... everything needs admin rights.

To surf the internet again with the computer I tried to install a new Windows but it´s seems to be protected with Bit Locker, asking for recovery key.

I´ve googled and googled bunch of CMD tricks but most of the shows "system error 5 has occured"

Is there anyway to get the wireless internet to work, change the admin or install new Windows? - or should I rather enjoying throwing it of the balcony or set it one fire? :)