Paint bucket, GreyScale help

i have two problems, when i create a new image its is automatically set to Grey scale, thats anoying but i can change it. then when i select black and use the paint bucket i get black screen (no problems) however when i go to select another colour or white for my brushes nothing appears. also if i use a black brush i cannot put another colou over it. also if i have put a black brush down and i paint around it my brush colour will darken from the original colour and eventually turn black. can ny 1 help me with these various problems

okay maybe if its set out a bit more logicaly il get a better responce...

here is what i do...
1.make new image
2. change grey scale setting to RGB
3. select paint bucket
4. select black
5.make image all black
6.select brushes
7.selct colour white (or any other colour)
8. start painting over black(nothing happens.)

new senario

1.make new image
2 select brushes
3. selct black
4.start painting (no problems)
5.select new colour
6. cant paint over black
7. paint around the black ( new colour darkends until it turns black)

now what is goin wrong and how do i change it back to how it was?

Grayscale issue: When you Select File>New, below the size of the image is the Mode of the new file. Change that before you open a new file, and it should remain in that setting every time you make a new file.

Paintbrush Issue: Before you paint anything, open the brush options palette (if you have 6.0 or later the options palette is located at the top of the window, anchored with the menu system). Check to see what Mode the brush is in. If its set to anything but Normal, change it to normal. Most likely you have the mode set to Multiply. This essentialy darkens everything you paint on top of. Well, since black is the darkest color, it wont change that layer at all. Same thing goes for screen. If you have a white background and try to paint with any other color, nothing will show because you cant make white any lighter.

If the Mode isnt the problem, check the opacity of the brush. Because you say you can paint with black, I doubt that the opacity is the issue.

If neither of these work, try reinstalling photoshop.