I've read the previous questions related to my same problem regarding the USB not booting issue and have tried everything from what was replied in those post's but still no luck. I will tell you everything I have done so far (If it helps in any way...)

1) Previously I had Windows 7 running on my laptop, where I downloaded the official torrent ISO (i386 desktop) and using Unetbootin I made a bootable USB

2) Restarted the laptop with the USB connected and IT BOOTED, then I installed it on my HDD(Internal) replacing my Windows 7

3) After installing it restarted and I took some time to explore Ubuntu after the log in, then went online and followed some website for the things to do after installing Ubuntu 12.04.....and then there were errors while installing some softwares and plug-ins. The error asked me to check if i was connected to the Internet properly....while I was surfing facebook good as always on an open Firefox. The same error comes when installing Ubuntu one.

4) so I decided to re-install Ubuntu thinking I had done something wrong during the installation (I'm installing from the same USB)...and it didn't boot. I checked the boot priority and it was/is set in USB first (as always). To say in detail what happens is when I restart the USB light flashes at start, later on stops and in the screen the installed Ubuntu 12.04 loads up for me to log in (meaning it's not booting from the USB).

By reading you can see that I haven't done much and I honestly didn't even touch the system settings to mess things up. As I have mentioned above I've tried everything in the previous post's in this related topic and it didn't work so I'm hoping for a new solution as a reply. Thanks in advance :) Edited: I wanted to add this >> I want to clean install instead of solving errors so please give a step by step guide. thanks for any help :)