Thinking of getting an external keyboard
Thinking about getting an external keyboard
Which one is grammatically correct and why?
Both are equally acceptable. In some contexts, thinking of might be considered slightly more poetic than thinking about; when sending a note to my sweetie, I'd probably write "Thinking of you!" instead of "Thinking about you!" Off the top of my head, though, I can't think of any cases in which one would be correct and the other flat-out incorrect.
'Thinking of' usually means 'considering'. 'I'm thinking of a new car' would mean considering replacing your current model, whereas 'thinking about a new car' is what you do when watching the adverts, without necessarily planning to buy one. (So 'thinking about getting a new keyboard' would involve "Well, typing would be faster, but it's another cable to tangle, and it costs a bit, and..."). But it's only a connotation, not a meaning, and don't try to apply it to your sweetheart!
I think about my life and i am thinking of my life. The second one can not be in simple present form . So i think the first one means you think about all moments of your life but the second one carrues a contemoray thought