(You probably can't anyway, it needs a working floppy drive.)
Before you start troubleshooting, check the heat sink on your CPU, be sure it's the right way around, seated correctly and has a good thermal contact with the heat island on the CPU. Also make sure you took the protective paper off the thermal material. If the HSF isn't on right, it could be the thermal protection circuits cutting in that's stopping it from booting up.
If it still doesn't boot, try a couple of simple things...
1) Strip your system down to bare minimum... CPU, 1 strip of RAM, Keyboard, system speaker and Video and see if it will start up. It will take a while because there's no hard disk or floppy, but it should at least get to the point where you can "hit DEL for setup"...
2) If #1 doesn't work, while it's still in bare minimum config, turn off power at the back of your system, hold down the END key (above the up arrow on your keyboard) while you turn the system on. This should take you into a "safe mode" startup where you can set your CPU, Memory speed and other functions.
3) If #2 doesn't work (not all motherboards support it) look in your user's manual, there will almost certainly be a CMOS Clear jumper on your board. Use it according to the instructions while still in bare minimum configuration and see if that gets you to the BIOS screens.
Once you get to the BIOS, put <i>everything</i> on auto detect --drives, CPU, Ram, Video, all of it. Now you can rebuild your system one drive/board at a time, testing to be sure it still starts reliably at each step. Leave all your settings on Auto and once it's working with your favorite OS for a week or two... then you can start tweaking, clocking and specializing your settings...
Should all this fail, you probably should consider sending the board and CPU back and getting replacements.
Flashing a BIOS is a risky deal. If anything should go wrong --and it sometimes does-- you will be left with a useless motherboard and may have to either return it or purchase a new BIOS chip. You should never flash a bios unless it is absolutely necessary, to fix a problem.
I would suggest reseting the BIOS with the jumper on the motherboard, if you cant find it take out your battery for 10 seconds then replace, if it still wont boot up then it may be your power supply, if you dont have a 300watt power supply or bigger with a p4, or AMD Athlon XP, it wont boot because it simply lacks power because of all the other hardware along with it, especially the graphics card which depending on which one you have can use some serious wattage...if you dont have a bare minimum of a 300 watt power supply you need to buy one, i suggest a 400 watt or better for a top of the line gaming machine...also check your power plug, if the power supply provides and the motherboard has the slot for a extra 4 prong plug for use in conjunction with the main power plug use it. Also plug in your Case speaker it will provide you with helpfull diagnostic error codes which will help you determine the problem.
I imagine these helpfull tips will solve your problem.
It's probably either a non-working or unplugged CPU fan. Or a badly mounted heatsink. It will shut down if the CPU fan header doesn't detect a certain speed, to prevent overheating. It may also shut down if the heat rises beyond a set point.
There's some other information in the first post of this forum that can be helpfull in troubleshooting installation problems.
<font color=blue>Watts mean squat if you don't have quality!</font color=blue>