Please post details of your system, "a blue light" doesn't offer much.

Your problem is either the power supply(PSU) or the mtrbd. to include anything on in/it/installed, etc.. Unplug the AC cord for 10min. then reconnect and power-ON. What are the results? If no go, then open side cover of case. Before this, if you have any warranty, use it as you may void it and/or take only the required action they suggest if active warranty. If none, proceed as you possibly fit it yourself. That's it for now, post back.

If you like, search the forums here as your problem is a common one. See the fixes, solutions often suggested.

tada -----Willy Happy