You need to read the UDF header better. The second parameter is required and should be 1 if you want to get the IP or 0 if you just want to check for a reply.

See :
 Code:
Computer(Required)
	-  String value representing the Computer to ping
GetIp (Required)
	-  If specified (1), the Function will Return the ip-address
		of specified Computer rather than pinging it ...
		Has to be 0 If you want to check For reply !
LoopCount (Optional but useful !)
	-  Integer value representing the number of times
		the Computer shall be pinged
Timeout (Optional)
	-  If ommited the Computer Gets pinged with the default
		timeout (1s) And default retries (4)
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