I need help with a dual boot!

I need help with a dual boot! Hi so before I start i would like to inform You that it is my first time posting i had just joined the web page and hope some one can help!
so i Built this custom computer in late October of 2018 and i have been trying every since to dual boot windows 7 with windows 10 i am currently running JUST windows 10 on my pc but i love windows 7 much more and i need windows 10 for a few of my programs. when i open up the .ISO file for windows 7 ultimate it starts as normally but when the system restarts i get the dreaded "Blue Screen of death" and the error code 0X000000A5 and i have tried every method in the book now i am currently only partitioning 1 500GB drive do I need a separate drive for a custom built PC. i am usually a pretty tech savvy guy but currently i am at a stale mate it so one know how to fix it it would be much appreciated.

Welcome to the forum. when you duel boot you install the oldest o/s first as if you do it after it wont understand modern boot.
is win10 using uefiand gpt disk?


The simple way is to use free virtual box and run 7 as a virtual pc as it doesnt effect boot up Downloads – Oracle VM VirtualBox

Actually, some may argue but IMO the simplest way is to take one disk out and install Win 7 on the remaining disk using one MBR partition only. Make sure Win 10 uses only 1 disk to boot up (take other disk out and see if Win 10 will boot properly). To boot into Win7 go to BIOS and choose legacy boot, for Win 10 choose UEFI boot. If you do it properly, each install will not interfere with the other and no matter how broken one OS is, you can always boot into the other. There is one issue: system restore will not work properly in this case, but I had issues with system restore for years now, even on single boot system, so don't rely on it anyway. Also make sure you can access BIOS with Fkey, as the newest MS way to access BIOS, recovery etc is the most stupid, ridiculous thing I've seen in long time, here is sample: How to Access the BIOS on a Windows 10 PC .

OK i'm gonna take a little time off for a week or 2 but thanks with every ones help!

MrMystery,

Before you try this, carefully read this entry.

Windows 10 corrupting removable hard drives. Work-around included! - Microsoft Community

You can also search terms like "Windows 10" "fast boot" "Windows 7" "data loss."

Mostly, be sure you turn off the fast booting feature in Windows 10. Be sure to check its status after you update it.

Also, have backups of your data files before you switch back and forth and know how to restore them. You will be a happier camper. I learned the hard way.

baumgrenze

baumgrenze is right, make sure you disable fast boot. Fast boot is MS fancy new name for old (I think since Win xp) hibernation and you can't hibernate OS, change drives and then wake the system up, since hibernation is broken and doesn't update drive allocation table on wake up, so it will corrupt replaced drive. I forgot about it because first thing I do on new system is disable hibernation, it's useless and has other huge problems besides corrupting drives, which I don't want to go in detail. If Win10 shuts down normally (no fast boot, no hibernation) you will not have any corrupt drive problems.

baumgrenze said:

MrMystery,

Before you try this, carefully read this entry.

Windows 10 corrupting removable hard drives. Work-around included! - Microsoft Community

You can also search terms like "Windows 10" "fast boot" "Windows 7" "data loss."

Mostly, be sure you turn off the fast booting feature in Windows 10. Be sure to check its status after you update it.

Also, have backups of your data files before you switch back and forth and know how to restore them. You will be a happier camper. I learned the hard way.

baumgrenze

Heard about this issue before but never thought it could cause heavy issue.

DavisHill said:

Heard about this issue before but never thought it could cause heavy issue.

Often the problems that we tend to overlook are the ones that cause the biggest problems.

Soooo i'm back
i just want Windows 7 already
is it possible to take the second SSD i have put it into and old tower and boot and install windows from there and when its done put that back into my main computer
please help me