If ALL channels are clogged/not printing with your 9800 after letting it sit unused for “over a month” (does that mean 3, 6, 12mo?), then I suspect you have something more than just dried ink going on, and likely have old/clogged dampers or other parts in your printer are old and need to be replaced.
Another thing you will need to consider is the pigment in your ink carts and internal ink system has settled, so will not print correctly- therefore you will need to shake your ink carts to get pigment in suspension, then run 2-3 Power Clean Cycles or one Initial Fill Cycle to purge settled ink and get in-suspension ink to your print head.
You should NOT use Windex or other ammonia cleaners on your print head or internal rubber parts (wiper blade, capping station), because while they can be good at quickly cleaning, they also quickly dry- which can make things worse!
Best of luck~ Dana