Google your model for instructions on how to remove or unplug the CMOS battery. Try resetting the BIOS by disconnecting the battery for a couple of minutes and then put it back and try it again.
Were you simply adding additional memory along WITH the memory that was already present, or were you installing it in place of the original module? I'd remove all the modules, reset the BIOS by disconnecting the CMOS battery, press the power button for thirty seconds, reinstall or reconnect the CMOS battery, reinstall the original module and try it again. Be sure to remove both the power cable AND the regular battery when resetting the CMOS battery and then reinstall them before attempting to power up again.