Crazy computer at certain times of the day!

Hello, PLEASE PLEASE HELP!!!!!
I am at my wits end I recently bought new laptop with vista installed......which was fine at first. Now from Mon to Fri after 4pm ish and all weekend my computer goes nuts.....I'll try and explain....first my internet will open by itself, when on iternent it will open pages i havent asked for, my keyboard will start typing letters i havent put, then it will just repeat the same letter over and over then stop..The my internet page will jump to the bottom of page constantly or up to the top..IT GETS WORSE....items from my desktop will start dissapearing or asking if i want to delete folders that im not selecting...like I said it runs brill through day and downloads really fast probs only happen at certain time.....WHATS WRONG?????????