First, try to isolate the problem. What, precisely, is not working correctly? Try to narrow down exactly what you expect to have happen versus what is happening.
For example, if your computer does not complete startup, you need to identify how far it gets, and write down any error messages. On an x86-based computer, if you get an error such as Missing operating system from the system BIOS when you start your computer, the problem is very different than if startup fails after the boot loader (NTLDR) starts. You know that the NTLDR has started when you see the message
NTDETECT V1.0 Checking Hardware . . .
Another way to isolate the problem is to figure out if there are related programs or functionality that works correctly on this computer. If so, what are the differences between what works and what does not work?