So I bought Samsung 850 EVO, 250GB, and plugged it into my Macbook (Mid-2010, Macbook 7.1). I installed it without mounting screws, because I don't have screwdriver to unscrew the ones from the old HDD (Toshiba, 256GB). I have on a USB thumb drive (16GB) installation of El Capitan, made using DiskMaker 5. Surprisingly, when I restarted the laptop and immediately hold the Option key, nothing happens except the blue screen and a cursor on it. There is no recovery screen or anything (that was actually supposed to happen). I then replaced the SSD with my old HDD and everything works fine as before. Anyone knows what might be the problem? I will go and buy the adequate screwdriver, but I don't know which one though. WHen I try manual installation through terminal I get this message at the end of the process:
Couldn't mount dmg /Volumes/Install OS X El Capitan/Install OS X El Capitan.app/Contents/SharedSupport/InstallESD.dmg (error code 112)Mount of outer dmg failed.