I used Pagemaker 6.5 and upgreded to Indesign CS5. My computer recently crashed and I am trying to reinstall the software but it is asking me for the Pagemaker serial number which I don’t have. 

Like the others, I’m going to tell you that the probability that you can get the software running is pretty much nil, but you should be able to log into your Adobe Account on Adobe.com using the email you used when you registered your software and recover the serial numbers.

I’ll be more blunt than the others. Even if you could install it, I don’t think you’ll be able to activate it. In short, unfortunately, it’s time to move on.

​@Cabling1 way back when (circa 2004) you could contact Adobe support to receive a special unlock code for this. One user said it involved holding Ctrl+Shift and double-clicking to generate a machine code you could give to support that they would exchange for an activation key. I don’t know if this is possible now, but you need to contact Adobe via chat support. Type AGENT to be connected to a live person. https://helpx.adobe.com/contact.html?rghtup=autoOpen

If your install of InDesign CS5 requires the serial number of PageMaker it was upgraded from, it’s unlikely anything can be done about it. Where do you reinstall InDesign CS5 from? A CD, online download etc?