Internet connection works for only a short time after startup

[yoshibear1009]

Hello, I've just installed Ubuntu a few days back for the first time, and all of a sudden yesterday, my network connection began to have problems. It works perfectly directly after restard, but only for 0~30 minutes. No amount of waiting corrects the problem, do its clearly not a connection/ISP issue. Other computers in the household connect as well, as long as mobile divices.
When I ping google/yahoo/anywhere when the Internet is down, it returns with

ping: unknown host yahoo.com

On a side note, another issue I've been having is that during boot, the screen goes black with a box stating 'Input not supported', and I was wondering if there was a way to fix that.

EDIT: I'm using a wireless connection, by the way.

Thank you for reading through my post
~Yoshi