I have an early 2008 mac pro with 2 x 20" cinema displays. Recently one of the power supplies failed which after replacing has been fine. Last couple of weeks after waking from sleep the display port closest to the motherboard has not worked for about 5 mins when after "detecting displays" from within system prefs it re-appears. It seems the port needs to warm up before working? Mac pro 2008 running 10.7.5 quad core intel xeon 2.8, 4gb ram ATI radeon 2600 XT 256mb.