When blower comes on flames go out what could be causing this

You don't mention what kind of furnace you have or how old it might be, some of the newer models will do this as a safety feature. If this is what your furnace is one of the things that cause it to do this is low air flow through the furnace. A dirty filter, a dirty coil, closed registers in rooms that might not be used.
There are other reasons but I find this one more often. If this doesn't help let us know.

You don't mention what kind of furnace you have or how old it might be, some of the newer models will do this as a safety feature. If this is what your furnace is one of the things that cause it to do this is low air flow through the furnace. A dirty filter, a dirty coil, closed registers in rooms that might not be used.
There are other reasons but I find this one more often. If this doesn't help let us know.
Its acarrier an its about ten years old