Hi Muesli

Welcome

Your code works fine
Since maciep is busy playing 'golf', I will give an example using division instead of multiplication.
I'm sure you haven't had the MOD operator available on Your TI83 but dig in and enjoy the strength of KiX

Code:
Break On
 
While 1
 
	CLS
	?"           BitCrusher"
	?"  Decimal to Binary Calculator"
	?"         Made by ???"
	
	???"  Decimal value: "
	
	GetS $DecVal
	$DecVal = 0 + $DecVal
	$EndDecVal= $DecVal 
 
	$BinVal = ''
	If $DecVal < 2
		$BinVal = $DecVal
	Else
		While $DecVal > 1
			$Bit = $DecVal Mod 2
			If $Bit
				$BinVal = '1' + $BinVal
			Else
				$BinVal = '0' + $BinVal
			EndIf
			$DecVal = ($DecVal - $Bit) / 2
		Loop
		$BinVal = '1' + $BinVal
	EndIf
	
	??"The Decimal number " + $EndDecVal + " In Binary is " + $Binval
	?
	?"Again? y/n" Get $Key
	
	If $Key<>y
		Exit
	EndIf
Loop

-Erik

ps.
The smallest code is not always the fastest