Bob,
Time to change the battery.
Most CMOS battery, even if PC is left on at all hours, will deplete themselves into a dead state.
It is an alkaline battery, not rechargeable.

Tim
 -------------- Original message ----------------------
From: Bob Gregory <[log in to unmask]>
> Setup:
> - Dell Dimension E510 will not boot unless CMOS battery is removed.  Works fine 
> after pressing "F1" upon BIOS warning.  With battery installed, green 
> motherboard LED is lit and power button light blinks amber.  Resetting BIOS but 
> did not have impact.  P/S is good.  Removed add-on components and memory to 
> isolate problem but nothing helped.  Remove battery and PC boots.
> 
> Any suggestions?
> 
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