I doubt it is caused by your CPU, the BOOTMGR is a file on your Harddrive (one that is needed to start windows. No OS can load without an apropriate
bootloader)
Start your computer, right away, start slamming on the 'Del' key (the most common BIOS setup key, if thats not it, it should tell you during POST itll say somthing like 'press *button* for setup') until the BIOS screen appears, if youve never seen it before, it looks somthing like
this.
move to the 'Boot' section (likley a tab near the top-right corner) and select boot device, make sure your harddrive is selected as the first one on the list (most people like to keep the floppy drive on top, but my rule is to keep the commonly desired device on top, in this case its your harddrive)
Now, for surefire testing reasons, change ALL entries on that list to your harddrive (yes, all to the same device) this will keep the BIOS from jumping out of order during boot, make sure that its looking for the bootloader on the right device.(remember that your gunna want to undo this afterwards, putting the list in origanal order but leaving the HDD at the top) now save changes and exit, your computer should restart automactily, if not then restart it on your own. It *should* boot.
IF IT WORKED:
the cause of the problem was your BIOS looking for the Bootloader in the wrong place. doing work under the case can often reset the BIOS, and even intalling software can do it, and UAC wont always catch it beacuse its not modifing the HDD. All that work just told the Bios where it was suppose to be looking.
IF IT DIDNT WORK:
Your windows installation has been coruppted, somthing you did or some program you installed (or a virus) or maybe even a glitch in the OS has gone and screwed up the Bootloader. Toss in the system repair disk and re-intall windows, sorry, its as simple as that. You can always try putting the HDD in another system and hope to recover any of you data for backup... but windows is guuna be a re-install.
IF WINDOWS WONT EVEN INSTALL
wheew, every roadblock in china eh? well if this is the case, your HDD is fried, or at least the Boot sector has been burned out, you said that this was on your old HDD, anything 4 years or older is just a bomb waiting to go off. Toss a new one in and re-install.
Thats my thoughts anyway,
-Tyler