Fans come on but system wont boot

[gumbone]

an MSI 740gtm-p25 mother board. fans and light come on but no beeps or video signal.
i bought a new 400 watt power supply. still doesn't work.

 

[knightdog56]

Give more details, is this an old system that quit working? or is this an update of an older system?

 

[gumbone]

fairly new system i got it last year. bought a bare bones combo mobo, processor, ram, and hard drive. it worked until now

 

[knightdog56]

What made you decide to buy a new power supply? Please list make and model of power supply. Also reseat the memory and the video card (remove and reinstall).