Hi Emma J and welcome to BC
When your friend's kids closed the laptop while it was running, it may have gone into hibernate mode. It saves your session so when you "open" up the laptop it will automatically resume where it left off. However, if there was anything plugged into the laptop (like flash drives, wireless bridges, etc.) and it was removed, then when you open up the laptop to resume, Windows thinks that the device is still plugged in when it's not. This can cause systems hangs and unrecoverable errors as it tries to "find" it.
have tried to do a clean install but that will not even work, tried installing Xp (formatting the partitions etc) then reinstalling Vista but still no joy. It either comes up with error messages like winboot.dll is missing and other error codes or it just wont boot up
Let me understand...did you try and clean install XP which was successful and then did an upgrade to Vista? Do you have an upgrade or full Vista DVD? Or did you try and upgrade using recovery media from Dell?