How do i upgrade my computer memory?

I tend to suspect the same thing here that he ended up seeing a bad burn to disk or incomplete write to a usb flash drive if the install was by flash drive(usb install key). I had a partial bad install here that took time to reveal itself however after a week's time. SP1 and several updates apparently didn't integrate into an iso as they should have.

Hangs when first installing Windows can be from bad ram as well as bad burns and why Memtest and Disk Check tools are the best first options to discover or rule out bad ram, drive errors from install, etc. Yet you can still see bad installs when everything is in perfect working order!

That was the case when removing a WD Green Power drive from an external casing it came in to install for internal use as an extra test drive for the 7 RC. Every program saw problems despite a reliable burn to disk! Once the next install went onto a Caviar model on the last build the RC ran everything like a champ.

As far as bad burns sometimes you run into bad media and toss coasters around trying to get one to see a good burn. If the hardwares(memory, hard drive) gets ruled out bad burns and bad installs come into focus.

Although the OP has not said so specifically, it appears that his computer is without an Optical Drive. The OP to elucidate. If my guess is right then please create another Pen Drive W 7 Installer and try again.

He might have a bad iso since he mentioned downloading it? (hhmmm...)

At this point we can only wait until he replies back with some system information and he has made out with this so far.