thanks for all your help guys.
eventually

I backed up my device (using N900 backup application on the phone.) to the memory card

reflashed my phone using OVi

restored backup.

everything worked fine. The backup even downloaded all my apps again .. wooohoo.

Also my battery life increased sooo much.

I used to get 6 to 8 hours of battery. I always thought this was cause I had my gmail,hotmail and exchange on 'alwasy on' sync VIA 3G.

But after reflashing, my battery now is more than 2 days. yahh


BTW, I did not reinstall any facebook apps.