Dell Dimension 4600 desktop memory upgrade

I hope that you checked and those 1G units are compatible with the slots...I mean if the pc supports 1G units...some mo Bo do not support more than 512 on a ddr slot...if the compatibility is OK ...try to see if inserting one unit in the slot where the 512 it id now ...make it work ...this will verify the compatibility too...if is working it means that they should work together too
so ...removing the bios battery was a smart move ..cause it needs to get t default optimal settings ...but ,,,cause we are talking about ddr 1...you should look for a setting that allow multiple slots too ...and also check the units compatibility to work in multiple units way...
after all that is done ...even if the pc do not sees the ram memory entirely ...I suggest to reinstall the operation system from scratch ...I do had a problem like this with an assus pc ...and after reinstalling it was ok ...

Well first the mother board needs to be capable of handleing that much memory you can check that by going to the dell website and checking the specs on that model pc or mother board if the bios isn't recognizing it the chances are it won't but take out the 512 stick and just try one of the 1Gig if it does recognize that then try the second stick if it doesn't recognize them both then chances are it can't handle that much memory.