I replaced the battery in my iMac g3 and took out the old memory card and put in 2 new memory cards, following instructions I got off the internet. When I turned it on, it beeped at me and its power light is flashing yellow and green. Help! How do I save it? Edited to add: I put the old one back in along with one new one. It made the "dong" startup noise, but the screen is black. Edtied again: I took both new cards out, and now it's happy again and back to OS 9.1. I wanted more memory to upgrade to OS X. What went wrong?