Additionally to what Tigsounds has said, if it is NOT password protected at the BIOS level, when the computer first boots up, it should show you 2 options if only for a second while the BIOS/loader are started. Try one of those options. If you do not see those options, try pushing one of the following keys repeatedly the moment you hit the power button. First is the F12 key, and second is the Delete key. If neither of those work, try the F5 key (i dont know why, but one of the people that programmed the bios for sony computers decided F5 was an appropriate key to make people push instead fo the industry standard.)
Good Luck!