I use a compressor to clean my PCs at home and at work, but you need to remove the fans first. When the system fans are dirty I just replace them. When the GPU fans are dirty I pay extra attention and clean the fins with a non-static foam cleanser and dry thoroughly before re-use. Do not spray any form of liquid in the fans, put it on a nice quality cloth (lint-free?) and wipe clean.

If your GPU chip is dirty you have some severe issues, as it means you have a gap under your heatsink. I would imagine you haven't, but if you do have to this problem. I would remove the heatsink, wipe carefully and apply some fresh heatsink compound.

All components can be cleaned to be honest, but you should make 200% effort to make sure you are protected against ESD and that you work in a nice ventilated area. Most important is to make sure everything is completely dry before re-use. I am qualified in electronics and can repair expensive networking and power equipment to board level. I have had to clean some horridly dusty and smoke damaged equipment before. I left them to dry infront of a fan for 48 hours and they still worked fine.

My last company used to bathe whole circuit boards for some USA Army Networking Kit in a cleaning solution and let it dry. Made em look new too! If you have ever soldered anything, it smells like flux cleaners! Just take care and if you are unsure, don't be afraid to ask for help.

Any problems let me know.