Safe in secret room

I cannot get the safe to open despite using help from walkthrough and forum. Does it need resetting in some way if you get it wrong if so how do you do it?
Thanks for any help.

There is a "safe in secret room won't open" thread on this page, which may be of use.

Light has just gone on in my head and I have realised where I have been going wrong, safe now open and I can continue.!!

Would you add your solution to the similar thread please, just in case it can help the other poster?