my tilde key wont work in oblivion and i tried 3 keyborads! help plz!!!

It might not be the tilde key, it should in theory be the one between tab and escape on most keyboards, it comes in many different varieties. Some people here my offer some possibilities.

Also note that it doesn't pop up with a box like it did in MW, just a little line to type things into, but it still pauses so if you leave the game unpaused watching something like water or moving grass then you can tell when it open.

I also tried it on my moms tablet pc and it works fine on hers but it wont work on my computer (hp media center m7334n):

athlon x2 dual core 2ghz
1.73 gb ram
250 gb harddrive
cd rw, dvd super multi + light scribe
ati radeon x300 se pci-e 256 mb
microsoft media remote keyboard
microsoft wireless laser mouse 6000
nec multisync 15 in xga monitor

Have you tried swapping the keyboards around? I know you wouldn't want to use a wired keyboard all the time but if you check if its the keyboard then atleast you'll know whats to blame.