Try to your install your build 7048 in a virtual machine to see if it's really your iso/files that are messed up instead of wasting your bandwidth downloading isos. If W7 doesn't install in the VM, then it's the iso(s). Otherwise, it's either a security software that blocks the install, the iso wasn't burned well, or burnt at full speed on a tired/too scratched DVD-/+rw disk. If you installed it from the hard drive, then something might have been corrupted when you extracted the files from the iso. It could be many things.
If your iso install fine in a Virtual machine like VMWare, start looking at what's installed on your computer and what could possibly cause an upgrade failure.
trying different iso doesn't do anything if the problem is caused by a third party software. Antivirus/anti-malware/firewall software have security that prevent their files from being removed, altered or deleted and it may cause problem during a system upgrade. Have you tried to upgrade after removing such software as I mentioned in the post above yours?