Why can't I use the Basic brush tool?

Question

I'm learning the ropes of drawing in Illustrator and I've fallen at the first hurdle. Why can't I use the Basic brush tool? Whenever I select the brush tool and use the 'Basic' brush type, the cursor turns into a hashed circle indicating I can't draw. If I load other brushes, I can draw with other brush types, but I can't use the Basic one. If I select the Basic brush when I have other brushes loaded and try to draw with it, it always defaults to a different brush! I don't understand why.
On a related matter, I'm also having trouble changing brush size. I know that using the [ and ] keys changes brush size, but I have no idea what the values are. If I try this in Photoshop, I can see the brush size in the Options bar, but in Illustrator it doesn't appear anywhere! Not in the Brushes palette, the Stroke palette or the Appearance palette. Where can I see the brush size?

Answer 1

Glitcher,
The following is a general list of things you may try when the issue is not in a specific file (you may have tried/done some of them already); 1) and 2) are the easy ones for temporary strangenesses, and 3) and 4) are specifically aimed at possibly corrupt preferences); 5) is a list in itself, and 6) is the last resort.
1) Close down Illy and open again;
2) Restart the computer (you may do that up to 3 times);
3) Close down Illy and press Ctrl+Alt+Shift/Cmd+Option+Shift during startup (easy but irreversible);
4) Move the folder (follow the link with that name) with Illy closed (more tedious but also more thorough and reversible);
5) Look through and try out the relevant among the Other options (follow the link with that name, Item 7) is a list of usual suspects among other applications that may disturb and confuse Illy, Item 15) applies to CC, CS6, and maybe CS5);
Even more seriously, you may:
6) Uninstall, run the Cleaner Tool (if you have CS3/CS4/CS5/CS6/CC), and reinstall.
http://www.adobe.com/support/contact/cscleanertool.html