I generally recommend that you purchase Dell computers although their reliability is generally no better than other manufacturers. You can see reliability ratings for desktop computers here or for laptop computers.
New computers are arriving with Windows 10, although you can still find Windows 7 computers available.
If you're just considering a tablet, David Pogue of the New York Times wrote an excellent article on how to choose among them.
Windows 10 comes in 32 bit and 64 bit versions. You can learn more about the differences between these two here.
Microsoft has announced that computers with Windows 7 and a Skylake processor will receive somewhat diminished support after 7/17/18
PCMag has an excellent article with lots of information about buying monitors.
Some computers are coming with Solid State Drives (SSD) rather than hard disk drives (HDD). SSD are much faster than the old HDD, although are several times more expensive. You can read an article that compares the pros and cons of each type of drive.
You will want to get word processing software (and perhaps spreadsheet software) for your computer. If you want to buy Microsoft Office, the least expensive way to do that is to buy the MS Office Home and Student Edition, which is widely available at Office Depot, Microcenter, and Staples for $149, or even less when it is on sale, which is frequently. MS Office Home and Student edition is also available on some, but not all Dell computers. Home and Student edition contains Word, Excel, and PowerPoint. There are other versions of MS Office, which you can compare.
Microsoft Office Online is a free version of Microsoft Office. As it's name implies, it includes free online versions of Word, Excel and PowerPoint. The online version is available here, and you can also read a detailed review of the product.
You can also get a product that is very comparable to MS Office called Open Office here. It is free of charge and has received excellent reviews.
You must have antivirus software on your computer, and I strongly recommend that you obtain antispyware software as well. I give you recommendations on the best packages for your computer here.
If you want to replace your Internet Explorer browser with a browser that is more secure, you have three good choices: Firefox (made by Mozilla) or Google Chrome or Opera.
If you need additional email software, Thunderbird is an excellent choice and it is free.
If you are shopping for a printer, you can see reliability ratings here.