I also facing the same problem with DH55TC. Hope DH55TC is one of the failure models. The very first day itslef my system got problem with same issue. Then the dealer replaced with a new one. After one month the new one got the same problem. Then the dealer sent the mohter board for warranty. After waiting 45 days I received a new DH55TC by replacing the old one. Then it was working arround one mounth with out problem. Now again it is showing the same problem.
So I am thinking of throwing away this DH55TC and would like to go for ASUS Motherboard. ASUS has better feedback comparing INTEL