If it's flashing that's because it doesn't have a lock which is why you don't have a speed stamp.
How long has it been left flashing away as sometimes the first lock can take a while.
Some cars have a coating which stops GPS receivers from working so as a test it may be worth sitting it outside with the writing facing up and see how long it takes to get a lock - if it just keeps flashing away there's the possibility it's faulty or you have the wrong firmware for that receiver. Were they bought together and if so where from?