It’s happened before: In 1859, sunspots erupted, causing sparks in telegraph offices that set paper on fire. Today, 150 years later, we are much MORE "wired," and sun flares are much more dangerous.
Satellites would be disabled. GPS and radio signals would be scrambled. Electricity grids could burn out, plunging the areas where the flares hit into darkness. Depending on the amount of damage, these outages could last intermittently for years.