Hi Tommy,
Well, it partly depends on the size of the solar flare. If it is a big enough one that there are lots of X-rays produced then that can effects on Earth, however it generally doesn't do much damage to spacecraft. The catch is a lot of big solar flares are associated with large, fast coronal mass ejections (CMEs) which can accelerate particles. Those particles can cause a lot of problems for spacecraft (damaging detectors, corrupting transmission signals, even confusing the spacecraft enough for it to automatically shut down) and even for astronauts. When the CME runs into the magnetosphere (the protective magnetic region) of the Earth, it can cause a geomagnetic storm. That, combined with the energetic particles can cause a host of problems in either in terms of communication, power lines, etc.
Best,
Christina