Bill Gatess first day at work in the newly created role of technology adviser got off to a rocky start yesterday as the Microsoft founder struggled for hours to install the Windows 8.1 upgrade. The installation hit a snag early on, sources said, when Mr. Gates repeatedly received an error message informing him that his PC ran into a problem that it could not handle and needed to restart. After failing to install the upgrade by lunchtime, Mr. Gates summoned the new Microsoft C.E.O. Satya Nadella, who attempted to help him with the installation, but with no success. While the two men worked behind closed doors, one source described the situation as tense. Bill is usually a pretty calm guy, so it was weird to hear some of that language coming out of his mouth, the source said. A Microsoft spokesman said only that Mr. Gatess first day in his new job had been a learning experience and that, for the immediate future, he would go back to running Windows 7. 