Since after the rapture, new believers will not be sealed with the Holy Spirit, What will be the role of the Holy Spirit? I dont remember where I got that information but I believe I read it somewhere? Is that biblical?
Yes, I believe the Bible says that tribulation believers will not have have the Holy Spirit sealed within them to guarantee their salvation. However He will still be very active on earth, convicting people of their sins and drawing them to the Lord. His ministry will be like it was in the Old Testament, and many millions will be saved.
For more information on the Holy Spirit in the Tribulation read, The Nature of Post-Church Salvation