Updated 03/31/14 – 1:29 p.m.

CHICAGO (CBS) — Illinois residents who don’t have health insurance yet have just hours left to sign up, or face a potential tax penalty next year, but they could have trouble signing up due to outages on the federal government’s enrollment website.

Midnight is the deadline for Americans to sign up for health insurance coverage under the landmark Affordable Care Act. Those who don’t could face a penalty on their 2014 income taxes when they file their returns next year – one percent of their household income, or $95, whichever is higher.

The HealthCare.gov website stumbled early on Monday — out of service for nearly four hours as technicians patched a software bug. The system came back up shortly before 8 a.m. Chicago time, then another hiccup around noon temporarily kept new applicants from signing up. The system, overwhelmed by computer problems when launched last fall, has been working much better in recent months and officials said it was operating at full capacity on Monday.

The site appeared to be working for some users by 1 p.m.

Health and Human Services spokesman Aaron Albright said more than 100,000 people were using the system at the same time when the site became overwhelmed.

When signing up, low- and middle-income taxpayers can get subsidies to help pay for coverage through health insurance exchanges run by the federal government and many states.

State officials, doctors, and hospitals have been making a push to get people enrolled so they can avoid the penalty.

At Norwegian American Hospital in Humboldt Park, there was a line of people waiting to sign up Monday morning. The hospital has helped more than 400 people enroll over the weekend.

Manuel Gonzalez, who works full-time but doesn’t have health insurance, was among those in line. He’s lived with the unknowns of having no health insurance for the past few years.

“You don’t know what to expect,” he said. “If you’ve got to go to the emergency room without healthcare, it could be pretty pricey.”

Lydia Vega was helping Gonzalez and others sign up for coverage. People seeking coverage see her as an expert on the complexities of the health care mandate.

“They’re asking basic questions, like they might get stuck on a question about income or dependents, and we’re able to help them a little better,” she said.

Bobby Rosenau, who also was in line on Monday, said he waited until the last minute to sign up because he was so busy.

“I wasn’t thinking about it. I didn’t think it was that important, but now I found out it was important,” he said.

There are only two exceptions to the Monday deadline for health insurance coverage. Those who have started the enrollment process can get an extension to finish signing up.

Also, those who have a “qualifying life event” – such as moving to a new state, if you get married or divorced, if you have a baby, a death in the family, or losing your job – also are eligible for a special enrollment period after the March 31 deadline.

The government says it will accept paper applications until April 7 and take as much time as necessary to handle unfinished cases on HealthCare.gov. Rules may vary in states running their own insurance marketplaces.

The administration is also offering special extensions to make up for all sorts of problems that might have kept people from getting enrolled on time: Natural disasters. Domestic abuse. Website malfunctions. Errors by insurance companies. Mistakes by application counselors.

To seek a special enrollment period, contact the federal call center, at 1-855-889-4325, or the state marketplace and explain what happened. It’s on the honor system. If the extension is approved, that brings another 60 days to enroll.

To sign up through the Illinois healthcare exchange, click here.

For plans outside Illinois, or other questions about the healthcare law, click here.

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