I have 450 routerboard, about 1 year old, and it appears to have died! The symptoms are that when first powered up the blue LED comes on for about half a second, and then goes out. The unit is totally unresponsive. I have tried 3 different power supplies.
I have exactly the same problem with one of our older RB450s - old enough to be out of warranty. I took it apart, and saw three of the capacitors humped (one near the processor with the heatsink, the other two are between the internal power connector and the Ethernet ports). I just bought three new capacitors, and will try to change them soon. I hope this is the only problem.