CHICAGO (AP) — The online insurance marketplaces that are at the heart of President Barack Obama's health care overhaul struggled to handle the wave of eager new consumers Tuesday, the first day of a six-month open-enrollment period that inaugurates the biggest expansion in coverage in nearly 50 years.A combination of high demand and technical glitches seemed to overwhelm the online system early in the day. Federal and state officials were working to address the problems, which led to long waits on government websites and a federal call center.As a sign of how ready Americans were to get started, Obama said more than 1 million people had visited the government's main website before 7 a.m. EDT — exceeding expectations and contributing to the delays.In Obama's home state, dozens of people who came to a Champaign, Ill., public health office to sign up for coverage found computer screens around the room flashing an error message: "System is unavailable."Kimberly Shockley — logging in from Houston, Texas — and Mike Weaver, who lives in rural southern Illinois, ran into similar glitches: They could not get past the security questions while trying to set up their personal accounts through healthcare.gov."I'm frustrated, very frustrated," said Shockley, a self-employed CPA. She spent more than an hour trying to get the security questions to work Tuesday morning without success. When she clicked on a drop-down menu of suggested security questions, none appeared.