Mi pi has red power light on and green light flashes , but tv display shows (no signal) message, i have a preloaded sd card from pi and all cables recomended but now i have no idea why it wont work. can you help
Do you have a lot of things connected to your pi's USBs ? I had the same problem than you and solved it by connecting only SD + HDMI + power on the pi, then reconnecting other device after the startup.
Also, please take a look at http://elinux.org/R-Pi_Troubleshooting for more information at how to solve your problems with the pi. There is a lot of information regarding troubleshooting at startup, among other things.