quran says in 3.77 that Allah will NOT speak with disbelievers on Judgment Day, but in 23.108, its says that Allah will SAY i.e. speak to disbelievers as : "Be ye driven into it (with ignominy)! And speak ye not to Me! isn't this a contradiction ?

All perfect praise be to Allaah, The Lord of the Worlds.  I testify that there is none worthy of worship except Allaah, and that Muhammad, sallallaahu ‘alayhi wa sallam, is His slave and Messenger.

First, you should know that there is no contradiction in the Quran as the Quran is the word of Allaah The Almighty which He revealed [to His Prophet]; Allaah The Almighty Says (what means): {Then do they not reflect upon the Quran? If it had been from [any] other than Allaah, they would have found within it much contradiction.}[Quran 4:82]

According to our limited intellect, some verses may seem to us to be contradicting, but in fact they are not.

Indeed, there are no contradictions between the two verses which you mentioned, praise be to Allaah. This is because may either be understood that Allaah The Almighty will not speak to them in a merciful way but with anger and wrath, or the meaning is that He will not speak to them at all; rather, it is the Angels of Allaah who would speak to them. Al-Fakhr Ar-Raazi said in his Tafseer (interpretation) about the saying of Allaah (which means): {… and Allaah will not speak to them…}[Quran 3:77]; that there are two interpretations for this verse:

1-      Allaah The Almighty will not speak to them in a manner that would make them happy, but He would speak to them in a manner that would make them unhappy as Allaah The Almighty Says (what means): {Then indeed, upon Us is their account.}[Quran 88:26]         

2-      Allaah The Almighty will not speak to them at all but He will appoint the Angels for their account. An-Nawawi said when interpreting the Hadeeth (narration): “There are three kinds of people whom Allaah will not speak to, and He will not honor them and they will have a severe punishment” meaning that Allaah The Almighty will not speak to them with pleasure like He would speak to the people who have done good. Instead, He would speak to them with anger and wrath, and he will not look at them; rather, Allaah would turn away from them, because His look to His Slaves is Mercy and Kindness.

Allaah Knows best.