How to prevent the garbage data when the serial port is initialised?
There are probably a number of reasons that might contribute to the problem that you are observing:


You are trying to send the string "Text" within the main loop without any delay between println calls. So the microprocessor is running at full speed and trying to send the string "Text" much faster than the baud rate can accommodate. The serial interface has a finite I/O buffer, which is probably filling very fast and overwriting old values in the middle of serial transmission. Hence potentially garbage characters.
Even when HyperTerminal is not running, the PC and Arduino are exchanging serial messages. So when you start HyperTerminal at some arbitrary time, the data in the serial buffer might not correspond cleanly to the start or end of a transmission.


As an alternative, you may want Arduino wait for a serial command from the PC before starting to send the serial data. For example, when using the Serial Monitor, you may send a key press to Arduino, which would then start sending data so that no data is lost while there is no body listening on the PC side or while a terminal program is not running.

Finally, flushing the serial buffers on either side of the serial connection might help you clear partial serial messages.