Possible suspects include network shares that are no longer available, and third party software that appears as a disk in Explorer. Sometimes such third party software tries to access hardware that is not present, and has a long timeout.
When it finally starts up, look for anything in My Computer that is not an internal hard drive. Disconnect any network shares.
To see a list of your network shares without having to endure the five minute wait, go to a command prompt and enter the "net use" command. You can then remove each share using the "net use /del" command. For example:
net use /del \\old_computer_name
net use /del x: