USB connected HD not getting recognized...

Sometimes it pings up after a few minutes of being connected... a lot of the times it's ignored.

i don't know if the system isn't looking or what exactly is going on, but this is kind of confusing.

when it gets recognized, it works fine;

Do you have access to any other computer? Is the behavior the same on another computer? For example, if you plug it into a Windows box and you also see erratic behavior, the drive itself may be suspect. This is my initial thought. How old is the drive?

Also, try connecting it to a different port, especially the keyboard one. This would eliminate the port as the problem or identify it as. What did you format it as?

Check Disk Utility when it's plugged in to see if it can find it. It may not be properly partitioned. I had a similar problem not too long ago about this.

update:
the drive is basically brand new. casing is a year or two old... the new casing i bought just didn't work with the mac, but my pc's HD casing did so i swapped them.

i plug it in, when it doesn't recognize it right away i just leave it alone. then the light on the HD case will blink. i then unplug it and plug it back in and *bam* its on. it pings right up. weird? weird!
i have no idea why it does this. disk utility says the drive is fine.