ACHI blocking installation

I have kept my W7 ULT running 32 bit just in case I needed to run legacy programs. This has not happened so to benefit from the 8 gig of ram, I decided to change to 64 bit. Of course this means that a fresh install is mandatory. The W7 ULT came with both DVD'S so no problems there. Early in the process everything ground to a halt, "installation was cancelled ---- Windows cannot install required files --- error code 0x8007045D". I thought that the 64 bit DVD was faulty so I downloaded the ISO and that suffered the same fate. Having nothing to lose, I turned off ACHI in the bios and Windows has almost finished installing. Since the other reason for changing is to use a new SSD, I will change back to ACHI after installation. Incidentally, the optical drive is an ATA unit due to a shortage of SATA ports.

How do you install using a DVD with the optical drive unplugged?

Update. Windows installed with ACHI disabled in bios, motherboard drivers, gpu drivers and activated fine. Then I set to windows updates and the machine continually locked up. I reset ACHI and decided to try another clean load of Windows. To my relief it has got past the original choke point and is loading noticeably faster. No changes to the bios have been made except the boot sequence and ACHI.

Start over and work through these steps to Troubleshoot Windows 7 Installation Failures - Windows 7 Help Forums
which resolve almost all installation problems and address the BIOS settings hanging you up.

I'd also look over these steps for Clean Reinstall Windows 7 which compiile everything that works best in tens of thousands of installs we've directly helped with here and has been used by over a million consumers without a single complaint.

Note how drivers are best handled in Win7 which is the opposite of XP: after getting online install all Important and Optional Windows Updates until there are no more offered, then import any drivers still missing in Device Manager.

I have got Windows to load several times but it locks up during driver installation randomly. The recovery screen does not work properly and control/alt/delete may or may not work. This pc runs XP,7ULT32,8.1PRO64, Mint 64 and W10 64 all builds to date all on the same bios settings with no problems. I have never had problems like this even back in the days of Win 95.

It's likely because you are still using Win95 methods on a driver-complete OS. I specifically mentioned how drivers are best handled since this is where many old-schoolers go wrong. Are you forcing drivers before seeing which ones Win7 wants?

Ive loaded W7 at least 10 times for myself and other people so I know a little about it. LAN drivers seem to be absent from W7 so its not quite so advanced as W8 or W10. Most of the failures occurred during loading as described in my first post.