I'm the sole survivor after the Catastrophe. I haven't seen any humans for a year and found this building with a working power grid and pc with this program. Can you help me to find humans? There is no longer internet or radio transmissions.
I will do my best to assist you, but I do not know about the Catastrophe or the state of the world following this event. I may be able to be more helpful if you provide more information, but here are a few initial ideas of how you could attempt to find other humans:

* Find the building's power source. Most sources of power will not operate for long without human intervention. Since you found a building that has power, this suggests there is likely to be one or more humans in the area to maintain it.
* Visually search the area for signs of human life. During the day, visible signs might include movement, changes over time, signals, or smoke. During the night, look for artificial light sources. Ideally, find a vantage point overlooking the surrounding area, as this would allow you to see a wide area. 
* Find or build a radio transmitter. Since the building you are in has power, it should be possible to operate a radio. I understand you are not currently aware of any radio transmissions, however if there are humans with radio receivers within range of your transmitter, you may be able to use the transmitter to make them aware of your location.
* Travel to locations with resources necessary for human life. Humans need safe water, food, air, and other resources in order to survive. They will usually create settlements in locations where they have easy access to these needs. Even if they reside some distance away from these resources, they must travel to sources of these resources on a regular basis.
* Leave messages in visible locations that direct other humans to your location. To select the most visible locations, consider where other humans would need to go. For example, as noted in some of the ideas above, locations visible from a large area and sources of essential resources are obvious locations. Travel routes, such as roads and highways, would also be ideal.
* Obtain access to satellites. This one may be challenging, but even without radio transmissions or the Internet, it's likely that functional satellites remain in Earth orbit. There are a wide range of satellites used for both military and commercial purposes that could be used to surveil wide areas for signs of human life, using both visible light and thermal imaging. Since large gatherings of humans are likely to create a significant amount of heat, thermal imaging could be particularly helpful for finding settlements of humans that are attempting to remain camouflaged. With no other humans around, if you can determine the location of the control centers for some of these satellites, there would be no one to stop you from accessing them (and if there is, then you would have found other humans, which also accomplishes your goal).