20X4 LCD Display Goes blank!

[poledust]

I have a Arduino Mega 2560, with a dht11, photocell, DFROBOT moisture sensor, 1307 real time clock, 2 four relay module boards, and a 20X4 LCD Display with back light.

The problem that I am having is the Display goes blank or the text gets all garbled, during start up or when I plug in or unplug the usb while on external power or not and when any of the relays come on one or more
but it does not happen every time at first I thought it was the 120v that I was switching on the relay boards but I put in some 12v interposing relays it did not change I then put a capacitor across the power to filter it did not stop this from happening I also soldered all the power to a little board thinking I had bad connections on my bread board did not fix the problem so now I think it might be a voltage drop the power supply that I am using has an output of 12 volts/2A and Im not sure if I am pulling to much power I don't have a amp meter capable of reading that low or that high of current.
Or do I have it wired right not sure I followed the adafruit tutorial and it works but am I missing any resistors not sure should I be using all sixteen pins not sure!
thank you any help you can provide!

[adafruit_support_bill]

These displays can get scrambled by spikes on the power line. The inductive spikes from your relays would be the chief suspect here. But it does not have to be directly connected to the noise source. I had one that would periodically go nuts. I finally traced the source of the problem to a compressor motor that was on the same shop circuit. Changing to a different circuit fixed it.

[poledust]

These displays can get scrambled by spikes on the power line. The inductive spikes from your relays would be the chief suspect here. But it does not have to be directly connected to the noise source. I had one that would periodically go nuts. I finally traced the source of the problem to a compressor motor that was on the same shop circuit. Changing to a different circuit fixed it.

Thanks I am pretty sure it is the relays most of the time. I will try powering it with a battery pack and see. Do you know if I should power the lcd not using the arduino. or do you know of any ways to clean up the power and stop surges like maybe I should buy a different power supply or put more capacitors across the 5v and neg power etc. do you know if there might be any problems with the library for these lcd's that would cause it to do this, just asking cause I am new to this! one more thing do you know if there is a better Lcd that doesn't have these problems.
Thank you for your help!!

[adafruit_support_bill]

Make sure that you have flyback diodes on the relays. http://en.wikipedia.org/wiki/Flyback_diode
Power supply filtering capacitors can help too.