It sounds as either the tab didn't knock off or the tab stop has been knocked out of place thus jamming the carriage. You can try gently pushing on the right hand side of the carriage towards the left next to the tab stop to see if it will know off. If it does, then it probably means you have a gummy carriage or the mainspring tension needs adjusted. Other than that you will probably need to have it serviced.
Answers & Comments
It sounds as either the tab didn't knock off or the tab stop has been knocked out of place thus jamming the carriage. You can try gently pushing on the right hand side of the carriage towards the left next to the tab stop to see if it will know off. If it does, then it probably means you have a gummy carriage or the mainspring tension needs adjusted. Other than that you will probably need to have it serviced.