You won't have to reinstall Windows Explorer because that's part of Windows. Anything that wasn't installed by Lenovo when the computer WILL have to be reinstalled. I don't know whether they installed Adobe or not, most manufacturers do, but not all. If you have files created by things like Office (Word, Excel, PowerPoint), MS Works, iTunes, your printer's software, antivirus software, etc. are possible things that might have to be reinstalled. Since I don't know what was originally on that computer or what was added in the subsequent 4 years, I can't be specific.