Old HP Pavilion a335w, mobo swap

I ve taken one of my familys old pc’s, And decided too upgrade it for them. I swapped the Mobo with a ASUS M2V-MX-SE, and a AMD athlon x2 4000+, I know they both work i had them both in a pc playing games last night. SO my problem, when i turn it on I see everything I should Post bio message, then would I like too repair or pick Windows XP too boot, And when I try too boot, the screen goes black and it restarts, and keeps doing this. Theres No video card, its only running 2 fans so could it be the fact that the power supply is 250watt? or is this enough? The PC had a pent 4. Thats pretty much all the info I can think too give, ask please for more, or give me an idea too what I do now.