Tense mix-up overload

Hi all,

This is my first post, and i really hope someone can help me here.
I was writing this piece, when it suddenly struck me that there seems to be little tense consistency in my writing.
For example, consider this (just a contrived piece):

"Nick sat down, thinking about all that had happened, wondering where it would take him, wondering if it made any sense to stay  any longer. He took out his cellphone and began dialing a number, even as a million doubts assaulted him. A loud song blared out from the speakers but he didn't take note..."

I've bolded the areas where I feel the conflicts occur. It really sounds alright, but does it comply to conventional English grammar. I mean, is it alright, or should I be doing something differently here.

I would be really grateful to anyone who could explain the rightness/wrongness of this style. I just can't seem to be able to make sense out of it.

Thanks in advance.

Thank you for the prompt reply Clive.

My doubt concerns the way I've changed the tenses in each sentence.

"Nick sat down, thinking about all that had happened, wondering where it would take him, wondering if it made any sense to stay  any longer. He took out his cellphone and began dialing a number, even as a million doubts assaulted him. A loud song blared out from the speakers but he didn't take note..."

Here, Nick "sat" is clearly a past tense. But right after the comma I've used "thinking", then another comma, "wondering", and so on. So my question would be, what tense are those parts of the sentences in? He sat down in the past, but this thinking and wondering, at what time frame are they occurring in? I hope I'm asking the right questions here, I'm not very good with the terminology. And the next sentence again starts in a past sense. And then, the "began dialing" what tense would that be, past progressive? Basically I'm really confused. A little explanation would help. Thanks a lot again.

hi
i think the text complies with conventional english grammar rules.i have found no mistake or strangeness

@Clive

That was a very helpful explanation. I never really considered the participles acting as adjective. Made a lot of things make a lot more sense :) . Actually I've always been a little cautious when mixing any kind of tenses and I'm never quite sure what combination is "acceptable" and what is not. I usually just try to read out the sentence and look to it that it "sounds" alright.

@macavalesi9

Yes, what you said actually makes sense. Using such a construct actually reduces the amount of redundancy in the prose.

Once again, thanks for all your help people. You guys rock.