Microsoft (NASDAQ:MSFT) has some explaining to do.

Last night, Mr. Softy reported $13.1 billion in fiscal fourth-quarter revenue, a 17% year-over-year decline, and more than $1 billion short of the $14.4 billion consensus analyst estimate. Per-share earnings fell to $0.34, from $0.46 in the year-prior quarter.

Full fiscal year revenue fell 3%, the first year-over-year drop in Microsoft's history as a public company.

The Q4 miss may have been inevitable. Microsoft fell $500 million short of revenue targets in Q3, and Chief Financial Officer Chris Liddell was so cagey during April's conference call that projecting Q4 must have been a finger-in-the-wind exercise for Wall Street's finest.

"Rather than providing a static quantitative revenue and earnings per share guidance, we recommend that you look at the market drivers of our business," Liddell said at the time, before digging into paragraphs of vague Dilbertian minutiae.

Blamestorming time!
To be fair, Liddell and his management peers likely didn't have much choice. Yet now, in the wake of a massive miss, it's time to ask what went wrong. Let's borrow from Dilbert and those DirecTV ads and blamestorm the answer.

Here's what we can't blame:

  • Bing, a good search engine that looks like the most serious threat yet to Google's (NASDAQ:GOOG) dominance in search and search advertising.
  • Advertising, because it's far too small a business for Microsoft. Online Services produced just $731 million in Q4 revenue, 5.6% of the company's total. Also, Mr. Softy is making needed moves to streamline and enhance its ad business.
  • Video games, because the Xbox 360 is still holding up well against Sony's (NYSE:SNE) PS3 and Nintendo's Wii. And that's even with the Entertainment division reporting a 25% drop in revenue.

That leaves the imploding PC market, a sinkhole that has sucked earnings from most of the industry's big players. Intel (NASDAQ:INTC) beat expectations, but still reported a loss. Advanced Micro Devices (NYSE:AMD) saw flat sales and more losses. Dell (NASDAQ:DELL) says its customers have been delaying purchases.

Microsoft's customers have been, too. Revenue in Mr. Softy's Client business unit, which is responsible for Windows, fell 29%. Operating income in that division declined 33%.

There's your answer, Fool. Surprisingly enough, when it comes to blamestorming Microsoft's Big Miss, it's Windows -- or more specifically, the scapegoat we know as Vista -- that takes the dart. Windows 7 can't get here fast enough.

Get your clicks with related Foolishness:

Start investing today -- just $7 per trade with Scottrade. Or find the broker that's right for you.

Nintendo is a Stock Advisor selection. Dell, Intel, and Microsoft are Inside Value picks. Google is a Rule Breakers recommendation. Try any of our Foolish newsletter services free for 30 days.

Fool contributor Tim Beyers had stock and options positions in Google at the time of publication. Check out Tim's portfolio holdings and Foolish writings, or connect with him on Twitter as @milehighfool. The Motley Fool is also on Twitter as @TheMotleyFool. The Fool's disclosure policy is vacationing in its seaside Italian villa next week. We'll be pressing the Fool's trading guidelines into service during its holiday.