1)
Why did Shmuel not say Hineni this time, and why did he not run?
1.
Malbim: He did not say Hineni, for Eli already knew that he is awake. He not run, for he was already embarrassed from the first time.
2)
Why did Eli say "Bni" this time?
1.
Malbim: Eli already had a Safek [if Hashem was calling to him]. He said Bni to show love, lest Shmuel be sad (that he bothered Eli for no reason), which inhibits prophecy.
