MacBook crashes during boot

I'm having the following problems:

- after latest El Capitan update, my Macbook Pro (mid 2010) crashes (turns off) during boot.

- I'm unable to boot in safe mode, the only way is recovery mode.

- I've run disk utility with ok results.

- I've done PRAM reset with no effect.

- I'm trying to reinstall El Capitan as a last resort but I'm getting the following error message: "An error occured while preparing the installation. Try running this application again."

Currently I'm really stuck in the middle of nothing, everything I've tried goes terribly wrong and I have no clue what is going on.

Please help,

Thanks.