Mobo doesn't beep and monitor goes blank when the welcome/login screen should appear

I was not sure where to post this because I'm not sure if it is a hardware or software issue. When my computer is turned off and I turn it back on, the first couple screens flash by (looks pretty normal), then the windows XP splash screen (I think thats what it's called), the one with the big 'Windows XP' and the bar with the sliding blue bars in it, that screen appears, then the screen flashes to black, then the splash screen appears again, then the screen goes black, but you can tell it's still illuminated, then it goes off, then back on to black, then off, and the green LED on the monitor starts flashing like the computer is off. I have to hold the power button until it shuts off, and repeat this process at least 3-4 times before the login screen appears and I can start windows.
I have tried changing my video drivers and reinstalling windows and chkdsk, and it does stat in safe mode (as far as I can remember), and the reason I suspect a hardware problem is that the mobo does not beep upon startup...ANy thoughts? I don't recall if the mobo ever did beep, and I don't know if every single mobo beeps. If somebody could offer some tips or a solution I'd be very appreciative! This is annoying the crap out of me, and I know it can't be good for the computer to keep starting up/shutting down manually so often.

Dell 4700
P4 520 2.8 GHz
512 Mb PC-3200 DDR2 (2x256)
40 Gb SATA HDD
Radeon X700 Pro PCE-e
MicroAdvantage DVD +-RW
Windows XP Home, SP2

 

How old is your Dell?looks pretty new check your warranty.

 

I got it maybe 2 months ago, so it is still under warranty (1-year).

 

Hell let them figure it out!