I just bought a Sony Vaio SVS15115FLB that came with Windows 7, after enjoying the PC graphic power for a little, I decided it was time to install Ubuntu 12.04.

First, I inserted a USB stick, reboot, press F11 but a message saying that no OS was found on the USB, so then I used a live CD. It booted fine and I installed Ubuntu, then when it was time to restart the PC, it didn't boot to GRUB but it went straight to Windows and it began an startup error and was looking for a solution, after it was done, it restarted and then it booted again to Windows and to the same start up error solution thing.

I freaked out, so I booted again the Ubuntu live CD, and installed Ubuntu over everything, after it installed I rebooted and then a message appeared saying Operating system Not Found, and I have no idea why. So I Googled again and found this post on Boot Partition, I did everything exactly on that post, but it didn't work (by the way, this was the message):

The boot files of [Ubuntu 12.04 LTS] are far from the start of the disk. 
Your BIOS may not detect them. You may want to retry after creating a /boot partition (EXT4, >200MB, start of the disk). 
This can be performed via tools such as gParted. 
Then select this partition via the [Separate /boot partition:] option of [Boot Repair].

It appeared the first time, then I did it all again and then it was gone. I rebooted and nothing, the same Operating System not found message appeared. So I decided to create a partition for Windows, hoping for something, but the message still appears.

I really have no idea what to do, but there is something odd, if I insert the USB stick containing Ubuntu 11.10, the message that says that there is no OS in the PendDrive flashes for a fraction of a second and the boot straight to Ubuntu 12.04 without problems (and booted to Windows when I installed it, ignoring Ubuntu), right now I'm using it like that, but its pretty annoying.

Can anyone advise me how to fix this? I'm no expert on this kind of things (boot, GRUB, recovery and stuff like that).