If u read Genesis the Holy Spirit was already present. God has
no beginning and no end. so Pentecost is not the Birthday of the
Spirit of God. It is merely the fufilment of Prophet Joel's
prophecy that one day God will pour out His Spirit upon all
flesh.
in the OT, there are instances where the Spirit came upon people to
empower and equip them for His service. The pouring of Spirit is
not a salvation issue. it is a service issue.
U r filled with His Spirit to serve and witness.