Why does my shortwave radio get all static-y whenever my roommate turns on her computer???
Because most PCs spew out RF (radio-frequency) noise as they operate. Anything electronic radiates *some[\i] electrical noise, and computers can be particularly bad, due to lack of adequate shielding. In addition, they can conduct noise through the power cord into your house/apartment electrical system.
Light dimmers can also be nasty in this respect, btw.
Most equipment is fairly insensitive to this stuff, but since shortwave radios are used to receive very weak radio signals, they’re especially sensitive.
There may not be much you can do, except for moving the PC and radio (at least the antenna) farther apart. If it’s being conducted through the power lines, you could try running the radio on batteries.
Here’s a site with a lot of info on computer interference:
ARRL on Computer EMI.
Arjuna34