Note: the term is "to go into bankruptcy", not "to go into bankrupt". "Bankrupt" is the adjectival form, so you can say "to go bankrupt" or "to be bankrupt", but not "to go into bankrupt".
Anyway, I'm no expert on the legal definitions of them, but basically "to go bankrupt" means to file for bankruptcy if you cannot pay your debts. Then there is the term "insolvency", which is slightly different. The term "to go into administration", however, refers to putting your company under someone else's control instead of liquidating the assets of the company (i.e. selling everything).