Well for starters check your 20 pin and 4 pin power connection. If they are both firmly in place then move on to your drives, are the ide and power cables plugged firmly into the hard drive and disk drive.Then check your memory is it in the right way and is it in firlmly, it should click into place. If so then check to see if your add on cards , if you have any, are in tight remove them from there slot, pci, pci-e or agp, and then re insert them firmly. Check to see that your cpu fan is plugged in tightly and running. Are you sure the monitor your using works. Also a little info on your problem would help. Do you hear the computer running when you start up? Does your mobo beep at all ? Try giving some specifics on the computer as well is it homemade or premade what company/parts are in the computer??