How to install windows on old first generation computers ? I insert disk but it can't boot ,what to do?

define first gen. computers have been around longer than you.
bootable disks did not come around til 90's.

You can't install Windows on an Apple I nor Apple II, nor an APF Imagination Machine, nor Altair, nor Imsai computers.  You still can't install Windows on an Ohio Scientific nor a Commodore Pet, nor a SOL 20 nor TI 99/4.

The first answer tells you the problem but he could have worded it in a nicer way. There was really no cause for that kind of reply as I doubt if he is all that tech savvy either.

Ron

Which version of Windows are you using?
Older computers will not take the latest version (10) or even 8,7,or Vista!
You may need to think about either XP or even a version of Linux like Puppy, Damn small, Xubuntu or Tiny Core.

You Need a floppy drive with CD-ROM drive in orden To start up Windows install program uf you want to install win95a or win31 o w311, from Win95b to win10 the cd or dvd disc has start up routine to install with nothing but the disc. 

When you talk about "early" machines, how early are we talking about?

Early computers used many memory models.  These memory models govern how much memory can be accessed by a program (and by the operating system).  Old Intel 8088 and 8086 boxes used Small Memory models limited to a max of 64Kb and didn't have advanced memory management capabilities.  Even the 80486 (the model just before the Pentium) was highly limited with a Medium memory (most of the time).  That was because program addressing was still based on using a 16-bit base address with SOME mapping capabilities.  But that wasn't really "advanced" memory management even though it was better than what MS-DOS could do.

A bigger part of the problem is that older machines were made for use when MS-DOS was the operating system and Windows was a layered (and swappable) application.  If I recall correctly, MS-DOS would run in 32Kb and still have a small amount of room. A 64Kb machine was heavenly!

I don't think you can run a modern version of Windows on any system that is not capable of using the Large (or perhaps Very Large) Memory model that would give you up to 3.5 Gb of RAM.  That is because starting with Windows NT, the computer's operating system became Windows, not MS-DOS, and that made the O/S very much larger than it had been.  The modules because segmented into formal layers in a way that required a LOT of memory just to boot up a system.

I remember some "moaning and groaning" every time a new version of Windows came out because the demands it placed on physical memory were astounding to us back then.  We often called Windows a hog because of its resource consumption.  And really, we weren't wrong.

not very tech savvy are you
 is that because you are uneducated or simply cannot read . It will say in big letters what computers it will work on and very old units are not capable of working with windows