Some of the questions you have do not have clear complete answers. Here is what we do know.
As LPChip's comment correctly stated, the /R/RE appear to be switches. In the traditional command prompt, placing a forward slash on the command line specifies the start of a switch. e.g., "dir/w" means to use the "dir" command, and specify the "/w" switch. (Switches are also called "parameters".)
In PowerShell, that doesn't work: you would need a space before the switch. The Registry is just a giant collection of data, so whether the space is needed, or not, would depend on what program is using that data.
Since you're being asked about installing the program, I'm guessing that the prompt is coming from "user account control" ("UAC"). So UAC is effectively protecting you from having the program be installed. Just say no.
Now, as for why that is happening for every reboot, that is something that I cannot readily say, but I can provide some advice for figuring this out. There are multiple ways that Microsoft Windows allows a program to start up. You can check the Startup folder (from your Start menu), but most likely you'll find your answer in the registry. Check out these keys in RegEdit:
- HKEY_CURRENT_USER\SOFTWARE\Microsoft\Windows\CurrentVersion\Run
- HKEY_CURRENT_USER\SOFTWARE\Microsoft\Windows\CurrentVersion\RunOnce
- HKEY_Local_Machine\SOFTWARE\Microsoft\Windows\CurrentVersion\Run
- HKEY_Local_Machine\SOFTWARE\Microsoft\Windows\CurrentVersion\RunOnce
That is probably how the program is starting.
However, although deleting that registry entry will likely stop the program from running, this doesn't answer the question of how the program keeps coming back after you successfully delete it. This is not very normal behavior, except if your computer is already compromised by malicious software (a.k.a. "malware"). If malware is re-creating the file, chances are good that malware will also re-create the registry entry.
So you probably need to find the malware. The easy way to do that is likely to run a scan with anti-malware software. If whatever you have installed doesn't work, try Malware Bytes (which is often good at finding stuff, and often works alongside existing anti-malware software), and/or other anti-malware software (although you may need to uninstall each anti-malware software before trying another, as multiple pieces of anti-malware software often tend to conflict with each other).
Hopefully that works; sometimes you need to do some more serious efforts to successfully get the machine cleaned, which may involve not booting from the long term storage device (e.g., "hard drive", "solid state drive") that you're using (because the drive you're currently using might be sufficiently compromised).
