If you cannot find isopropyl alcohol, go to a pharmacy and get a bottle of "doctor's spirit". Use it sparingly to soak a cotton wad and clean the TIM.
For the rest of the PC components, disassemble all parts --> use a soft brush to gently get rid of the dust, then give it a good rubdown with a dry microfibre cloth <-- for fan blades, use ear wax cleaning sticks (stick more cotton at the end of those if required).
For the cabinet, take out all components, sit the cabinet with side panels off in front of a table fan and put it on max speed - will get rid of a ton of dust. For the nooks and crannies (there will be many), use the brush and fibre cloth.
You will need lots of time and lots of patience - don't hurry it.
I am sure you know how to re-tim, but just in case you don't, google - there are lots of articles, videos out there (in fact, some on this forum as well I guess).
If you must use a vacuum cleaner, use a hand-held one (and not the bigger ones). Use more of the blower than the suction functions. Do not use on electronic components, use only on chassis, disk cages etc. After you are done with it, ground the cabinet to rid it of static shock.
If you can, do the cleaning during a highly humid time of the day.
Edit: Use a good quality brush, cheaper ones might leave behind their bristles on the pcb. Always check for these bristles and remove them before you re-assemble your stuff.
