1) the "wallet master key" cannot be exported with dump_private_key .. only with the in-app backup functions (that why we have that feature in the wallet btw)
2) you can only export the account owner key for a account - unless you made market transactions, the owner key is sufficient to regain access to the account
3) a account master key SHOULD NOT be imported with the "import WIF private key"!!! but using the console as described in http://wiki.bitshares.org/index.php/RecoveringFunds
4) is your account name registered on the blockchain?
5) if registered account name: go to console and type "wallet_import_private_key PRIVKEY"
6) why would you DELETE a wallet!?!?! ALWAYS keep a backup!! it's just a few 100kilo byte .. print it on paper if you don't have a usb stick