Before doing any reinstall or recovery, I would make sure your work / data files are safe. I see that you are new to computers so the following might be a little more than you want to attempt. You may want to get a tech savvy friend to do this for you.
1 Pull your hd and slave it to the system you are using now. Copy whatever you need to keep.
2 Reinstall the drive in the problem system.
3 Before attempting another install, it would be a good idea to check both the hard disk and the system memory. These are checked with apps that run from bootable CDs; no need for an os to be installed. I would use
memtest86 for checking the memory. The maker of the hd will have a diagnostic app on their site to check the hard drive.
Once you are sure the hardware checks out OK, then we can attempt to do an install.