(1) need to provide what your system components are.
(2) Is this a new build or was the system working and this just stared.
(3) for a new build;
a) Do the fans turn
b) Have you verified that all power is pluged in, 20/24 pin connector, 4/8 pin connector, Does your graphics card (unk type) have a 6 pin connector and is it connected.
(4) for an older computer, does the hard disk sound like it is booting into the operating system.
I think there is a sticky on troubleshooting a computer that will not power up.http://www.tomshardware.com/forum/261145-31-read-posting-boot-problems