|It is important that we see specs on motherboard and RAM.|
It is possible that they are not fully compatible, needs some settings changed, or even possibly a BIOS update to fully support the extra RAM or even newer density RAM chips on the sticks that you purchased. It is possible that the new RAM is significantly different than the original as to be incompatible together. As to the no longer recognizing the old RAM as it did before, placing the new memory sticks in auto detected a change and and the auto settings need to be reset or manually set. Adding a second pair of memory stick is best done with the same size, speed, latency, and where possible, the same memory chip type. When at all possible, the same brand, model, and exact series makes it the most compatible when possible. Some boards and some combinations are more finicky than others.
Do NOT try changing anything yet, just supply the specs and we will make more direct suggestions that will be more helpful.
You have to be a little bit crazy to keep you from going insane.