Also, in reality, you actually power more stuff up, once you are in orbit, than what you power down. In the first 2h50m of the mission, you launch and then reconfigure the whole inside of the Shuttle for being in orbit. Everything you don't need in orbit, is powered down. Two computers out of five are even shutdown in orbit. Only two GNC and one System Management computer are left, one of the Shutdown computers acts as hot spare for GNC, and is usually powered up during rendezvous and docking. Many navigation sensors are no longer needed until landing, and thus powered down. At the same time you power up such important stuff as the space toilet and the galley (the kitchen and sink of the Shuttle). The airlock is activated, the satellite antenna (Ku band antenna) as well. The star trackers can be used and are powered up...
The whole transition from launch configuration to orbit configuration is in a special checklist, the "Post insertion" checklist.