UDK re-install won't work

[neavah]

I recently installed the newest UDK version (2012-05).
Everything was installed and working fine. After mucking around in my game files (dev/src/mygame/classes/) something went wrong - I tried to revert the changes (I copied all my orignal, working files) but replacing the files back to what previously worked didn't fix whatever it was that I mucked up. Ultimately, I decided to uninstall and re-install.

I unistalled (add/remove hardware) and then re-installed
I'm on xp 64, so I have a shortcut to the install with '-progressonly' and (what I did the first time) after it does its magic, I manually restart (.net or dx installs/updates, I'm not really sure) on boot up udk installs and opens up

On re-install though, when I restart nothing happens (first time it auto started).
I go to the /binaries/udklift.exe and start from there.
On the loading screen I get a "run as" window asking me which user account I want to use to run this program. I never got this message the first time I installed, and to be honest, I have never been asked this to run any programs on xp/my computer

If I run as my 'current user' (\administrator - "this option helps prevent programs from using administrator privileges to harm your computer...") I get to the licensing agreement, agree, then "UnSetup has encountered a problem and needs to close"

I'm slightly confused as to why I am getting the "run as" dialog. As mentioned, I did not get this when I installed the first time (or past versions of udk)

I was hoping someone could give me some insight/help as to what I can do to get the latest version working again.
Is there some better/special process to uninstalling/re-installing that I missed?

I have uninstalled, and re-installed numerous times now, nothing has changed.

I appreciate any help I can get!

[reinrag]

I would first suggest to get an md5 checksum and compare it with the one on the website, just to check

[neavah]

Thanks for your reply!

I ran checksum as you suggested (calculation, then verification) on the UDK/2012-05 folder (it was the udk folder I should be checking?):
"Source checksums match actual, files not changed"

I'm not sure what you mean by 'compare it with the one on the website' is that just the verification (in the program)? (my appologies, before today I have never heard of this program, so I am not sure if I did things correctly)

Edit: I checked the UDKInstall-2012-05-Beta.exe with checksum, and compared to the udk download site, and they are identical.
I have tried installing 2012-03 version, and I get the same problem. Everything appears to be installing fine, at the very end it says something around the lines of 'starting up' and hangs at 'binaries/instaldata/manifest.xml'
then it closes.
I'm not sure if there's something to do with this file that is causing my problem.
I have the 2010-05 version installed, and working - in case that makes any difference (installed in 2010)

Thanks again for your help!

[neavah]

problem (somewhat) resolved.

I uninstalled, and did a system restore to a point before I installed 2012-05 (the first time). (For some reason there was 3 semi-installs of 2012-05 after the system restore...)
Either way, .net re-installed (maybe it was a problem with .net? idk) and the install worked.
...I don't seem to have a default inventory now (play in editor) but, at least it's running