I'm having some problems with booting on my old laptop. It is a Dell Latitude 1525 with an Intel Celeron CPU (550 @ 2 GHz) with 4 GB of memory. It used to run Windows Vista, but due to issues, I replaced it with Windows 7 32-bit, whic didn't run too well. I then tried to make it better by installing Lubuntu 16.10. Using Unetbootin, I put the ISO on a flash drive, booted from it, and managed to install Lubuntu without issues. Then, I installed some drivers for WiFi and printers, so there's no problem there. I chose this OS due to its low memory usage.
The issue right now is booting. Sometimes, it manages to boot up quickly, but other times, it just boots up and hangs on a dark screen. It takes so long to boot, I had to manually shutdown power to the computer, and once I restart it, it loads up with a choice between Ubuntu and Memtest. I chose Ubuntu and it runs through various checks, and then it hangs, so I have to turn it off manually again. This keeps on going for while until it boots up fully. I'm unfamiliar with how OSs work in general, so I was wondering why it has trouble booting up most of the time as well as wondering what I can do to make it boot successfully every time. I'm not sure if this information is enough, so please let me know if I need to provide more info to help.