I uninstalled FO3 because I wanted to put it on my new HDD and to clear out some old mods. Everything uninstalled ok but when I went to install the game again my computer freezes when the disc is inserted. Sometimes I can get the launcher to go if I open the CD tray and then close it again but it always hangs on a Direct X file ending in _25_x64 or something like that. I tried using the SecuROM diag tool but it didn't find anything useful, I tried using just setup.exe but its impossible to get to the point because my computer just locks up until I remove the disc. Confused I tried to install it on a different PC and the same issue occured. The disc is brand new no scratches, smudges or dirt. Short list of what I've tried is

Using SecuROM Diag tool.
Rebooting and shutting down.
Using setup.exe (even the 1 time I got there I still hung on the direct x file)
Install as admin.
Install on admin account in safe mode.
Delete temp files
I tried copying the disc to my HDD but it once again locked up on that direct X file.
Changing the compatibility of the setup.exe.

The funny thing is the game has worked flawlessly to install twice before. The first time I installed it I installed it to the default location and FOMM couldn't be installed there so I had to reinstall in a different folder. Now the game can't even be read without a lock up.

The only thing I can think of to suggest is to check around for a friend with an external DVD drive to borrow, and install from that. A conflict may exist between your drive and something similar to SecureROM on the disk. It happened to me, and I ended up using a Read-Only drive on an old PC left on the network to run my old LaserJet printer, from across the LAN.