It's probably a driver issue.
You could look in the Ubuntu control center and see if there's an item for "Additional Hardware" (There used to be, I know). Clicking that might identify the issue. Be sure to do it with the wired connection enabled in case you need to download something.
There are diagnostics you can use to identify the wireless chipset. This post, though it's primarily about Broadcom, lists them
Once you identify the chipset, you post it back to this thread and someone will be able to help you.
If it's Broadcom, the rest of the post will also help you.