We will need more information before making any suggestions.
How does the use of Serial.begin relate to your LCD display. Since you mention that the display displays 'random stuff' whenever you use Serial.begin that implies that it displays correct information whenever you don't.
So:
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What type of interface are you using between your LCD and your Arduino?
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What are you attempting to do with the serial interface?
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Is the 'random stuff' truly random or is it the same every time?
Don