Compaq presario v6112au
Motherboard problem

My laptop is not booting up..when switched on..lights come up..fan is working..cd/dvd drive ejectable..nothing appears on the screen..it restarts itself after about 20 seconds..and this cyle conitnues..

hp customer care people agreed that this is a mother board manufacturing fault but they are not offering free repair for my model (compaq presario v6112au; serial number: cnf6524y61)..

don't know what to do..any help would be appreciated..

thank you..