Is prayer valid with a drop of blood on the nose that has not fallen?

Slight nosebleed does not invalidate the prayer. In fact, al-Baji transmitted the consensus of the Companions that prayer is not invalidated by nosebleed whatsoever. Your prayer is valid, and you do not need to repeat it. Slight blood coming out of the nose is not considered an impurity that invalidates prayer, nor is it considered excessive blood that nullifies ablution. The preponderant view is that blood coming out from orifices other than the two private parts does not nullify ablution, even if it is excessive. It is recommended for one who experiences a nosebleed during prayer to remove the blood as soon as it appears. Sa'id ibn al-Musayyab and Salim ibn Abd Allah prayed while blood from nosebleeds flowed from them, and they did not perform ablution.