Everything is fine now. Thanks a lot for your kind help, I learned a lot during this problem.
Actually the problem was not there as such-- Windows was not loading from pre-formatted HDD's which i used to use on old computer with totally different configuration (Intel mobo and P4 with DDR1 RAM).
I had to reinstall Win 7 and voila. -- It installed smoothly and now system is booting fine and windows running ok.
I think when one changes mobo, the fresh OS install is reqd, and due to some configuration change it may become necessary.
Though one stick of RAM showed errors, i gonna RAM the kit.
Thanks.