I work in an office and sit 8 hours infront of a computer. the tower is below the table can the heat generated cause damage to baby during pregnancy?

No: Nothing to worry - the heat is minimal - most of it dissipates quickly.

Baby insulated: Your body and the babies bag of waters insulate the fetus from external heat/cold etc. Your body will perspire as needed to keep your body at normal temperatures & that keeps baby in a stable environment. The same goes if you are in the cold, you may feel the chill but as long as your body temperature stays normal, the baby is unaffected.