The consumer Windows PC and tablet market didn?t get the boost it needed from the launch of Microsoft's Windows 8 in the U.S., a research firm says.

Since the Windows 8 launch on October 26, Windows device sales have fallen 21 percent versus the same period last year, according to research company The NPD Group. Notebooks, which have been weak throughout most of 2012, saw that trend continue as they fell 24 percent. Desktop sales have fared better this year, dropping just 9 percent.

"After just four weeks on the market, it?s still early to place blame on Windows 8 for the ongoing weakness in the PC market," said Stephen Baker, vice president of industry analysis at NPD. "We still have the whole holiday selling season ahead of us, but clearly Windows 8 did not prove to be the impetus for a sales turnaround some had hoped for."

Since its launch, Windows 8 has captured just over half (58 percent) of Windows computing device unit sales, compared to the 83 percent Windows 7 accounted for four weeks after that launch. Windows 8 tablet sales have been almost non-existent, with unit sales representing less than 1 percent of all Windows 8 device sales to date.

"The bad Back-to-School period left a lot of inventory in the channel, which had a real impact on the initial sell-through rates for Windows 8," said Baker. "The strong performance of Windows 8 notebooks with touchscreens, where Windows 8 truly shines, offers some reason for optimism. These products accounted for 6 percent of Windows 8 notebook sales at an average price of $867 helping to re-establish a premium segment to the Windows consumer notebook market."

Average selling prices of Windows computing devices have jumped significantly this year. Last year, overall ASP was $433 while this year's ASP over the past four weeks has risen to $477. Windows 8 notebooks have seen a nearly $80 rise in selling prices versus the prior year, propelled by the aforementioned strong performance of touchscreen devices and a solid uptick in the pricing on mainstream notebooks. Windows 8 desktop ASPs were also strong with selling prices up nearly 10 percent, driven by the same factors as notebook sales.