Dell 4700 not booting

My Dell Dimension 4700 won't boot up today. It worked ok yesterday, no changes have been made since it worked. It doesn't load windows, just goes straight to black screen with white flashing cursor in top left hand corner. No beeps even with speaker turned on. Diagnostic lights are A green B green C yellow D yellow. Handbook suggests this is possible expansion card failure, but no card fitted. Help! Thanks.

 

Test you HD

 

Open up the case to be sure you do not have a sound card or a video card. If a card is present, reseat it and try to boot up.

 

I've tried that - no change

 

I only have the one computer - how can I test it?

 

Your two posts are unclear. Do you have a sound or a video card or both?
Since the lights indicate a problem with an expansion card remove one or both and boot up.

 

Just a thought do you have any bootable CDs around? You might try booting to a CD (like an installation CD) to see if that starts up. That would rule out an MBR problem which I associate with the blinking cursor.

Also if you have any USB devices plugged in then unplug them and see if any change.

I know the manual says the diagnostic lights are associated with a card but I would still try a bootable CD.

 

I removed all the USB leads and the computer now works. There appears to be a problem with one USB lead which stops the computer booting. Many thanks for all the suggestions offered.