I have an HP Pavilion dv6 laptop which initially came with windows 7, runs on Intel core i5,has 4GB of RAM and 640gb of hard disk space.Few months back i installed windows 8 on it. But finally i decided to make a complete switch to Ubuntu 12.04 LTS (i.e. without a Dual Boot). I got an ISO of the amd64 version (which I am not sure would prove to be a catch in my situation). I burned the ISO on a USB using the Universal USB tool.The installation proceeds smoothly, completes and asks me to reboot.Once I do that,all I get is the memory test running,finishing and then starting all over again.When I reboot and press Shift to view the GRUB, Ubuntu is not on the list and the only thing is the "MemTest" (which I think is the reason why the memory test is running indefinitely).Please Help.
If I were in that situation, I would redo the installation from scratch.
If you want to experiment a bit, load the rescue CD, drop into a root shell and try to re-grub the system again.
Another thing that I might do is load the rescue CD, drop into a root shell, mount the boot or root partition of the system disk (depending on how the installation was done) and see what is in the boot area, to see if a valid kernel is present, and then check the grub to see if the textual boot options menu is ok. You might try to fix the grub memu if that is all you find is wrong.
I have run into this sort of problem before, and Boot-Repair would probably work.
As per this page, just enter these commands into terminal (Default shortcut is Ctrl+Alt+T) to install it on a Live CD.
This will add it to your repository and then install it, and then run it. All that is required is that you have it run the "recommended" repair, and once it's done, just restart your computer without the Live CD.