A solid green light indicates connectivity is present. This link light is generally either green or off. Green is good, off is not! That light should stay a solid green. If you see it flashing green, that's a sign of intermittent connectivity, which is a fancy way of saying "one minute the PC is on the network, the next minute it's not". Most likely, either the NIC or the cable connected to the NIC is going bad. With the green light, flashing is not desirable.
Flashing amber lights indicate collisions. You'll see this flash occasionally even on a healthy network, but you don't want to see it flash so often that it looks like a solid amber light!