new memory for Powermac G4

I just installed (2) 512 MB DIMMs in my G4 for a total of (4) or 2GB. When I turned on the Mac it beeped, and the on/off light button blinked twice every few seconds. Also, the monitor didn't come on even after 30 minutes. Taking out and switching the 4 DIMMs changed nothing. What can I do to turn on my Mac? Thanks.

John Willetts
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