Really. You don't need a fancy computer to write a book, the most popular novel of the last twenty years, Harry Potter and the Sorcerer's Stone, was written on a yellow steno-pad. On The Road by Jack Kerouac was written on a roll of toilet paper. Hemingway wrote on a typewriter. The majority of best selling novels through history were written on basic technology, the majority of those using pen and paper.
The best writing instructor I ever had made us do all of our composition in MS Notepad so that we couldn't worry about formatting, font, pagination, word-count or anything other than our writing. That's my recommendation. Write in Notepad. When you're finished composing, edit in a word-processing suite like Word. You'll write better for it. There's nothing there to distract. There's nothing there but your words. That's all you need and more than that is usually a detriment to the product. Publishers have people they pay a lot of money to make it look pretty; they're paying you to put words on the page.
When I teach writing courses for prose or poetry, I forbid my students the use of anything fancier than Notepad. Fancy writing software suites make bad writers and do nothing to improve the work-output of good ones.
Also, disconnect your internet and take the phone off the hook. Writing time is writing time and should be protected from intrusion. When the words stop coming or you start to make mistakes or feel compelled to go back and edit what you just wrote, hang it up for the day.
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