Thirty-one per cent of users reported problems with upgrading to Windows 7, according to a survey of more than 100,000 customers by consumer helpdesk firm iYogi.
Some 9% said installations froze two-thirds of the way through due to a bug that requires changes to settings so that the computer ignores plug-ins.
The most common post-installation complaint is that basic programs such as Mail, Movie Maker and Photo Gallery were missing.
Windows 7 deletes these programs and makes users download them from the Windows Live Essentials website, which 26% of survey respondents said was confusing.
Some 8% said DVD drives could not be found, 2% could not sync their iPhones with Windows 7, and 14% said the new Aero theme did not work, mostly because their computer did not have the required graphics capability.
Once the bugs from upgrading have been worked out, users have had a relatively hassle-free experience and those who bought a new computer with Windows 7 preloaded have had the fewest issues, said iYogi.
Analysts said although there are a few bugs, no major problems have been reported and unlike its predecessor, Windows 7 appears to be a success for Microsoft.