Another Printer Problem!

[#1]

I have an hp deskjet 3930, when both colour and black & white cartridges are installed it won't print, the light just flashes, if I take the colour one out (which is quite new and has printed ok up until now) it will print with just the black.  I've searched for solutions but nothing has worked, does anyone have any ideas that I could try please?

[#2]

I don't have a hp printer but if it uses chipped cartridges could there be a fault in the chip .?
If all else fails it might be worth trying another cartridge.

[#3]

mixing old and new chipped carts, there not compatable and have to use the same generation chips for the printer to work properly (its about the flow rate control settings for the print heads being different)
your best bet would be to walk into pc world (or similar) buy two cartridges (keep the receipt and box) take the printer to them and say why don't it work, they will get you a set of carts off the shelf that will work or give you back the money as the product is defective