OLD Database error

I upgraded my website to the latest one.
I sort of deleted everything as I’ve backed it up…
and they sort of ‘restart’ everything for me…

the blog appears ‘new’..
with the default theme & the ‘welcome to wrdp’ post kinda thing…

I wanted to use back my old Database… so i did what we normally would do when we install a new Blog… I change e DBname in the config.php file.. to my old DB file (which still exist) and my website just simply turn b.l.a.n.k… my admin page flew out of e window as well. *sweat*

this happened a few times already..
1. when i upgrade it.
2. when I delete everything & try to upgrade again.
3. when I reinstall e files again.

it just keep going poof! poof! poof!
so.. u could see how desperate i am now.. that I even finally resorted to e forum for help… really dun wanna bother u guys… but.. guess i suck at this big time…