There are many reasons why Microsoft is failing.
1. Give customers what they want. If consumers wanted a tablet interface they would have purchased an Windows Mobile or iOS. Hence, why most people hate Windows 8 on their PCs.
2. Microsoft should adopt a more flexible business model giving consumers the right to use their software products for free if they agree to accept advertisements - for example during bootup/shutdown or on the desktop. A lot like how Google derives their income.
3. Microsoft has to accept that they missed the mobile and tablet boat. Google and Apple already own it. Xbox is doing well and until the next big thing arrives MS should concentrate on their existing product lines but at the same token be ready to learn from their past failures. A lot like how Blu-ray was a success and Betamax was not.