do you will you

We may say
1. Did you buy this computer? (past tense, it means那次你有無買this computer)
2. Have you bought this computer? (present perfect tense, it means 你有無買this computer)
3. Will you buy this computer? (future tense, 你會唔會買this computer)

We seldom ask 'Do you buy this computer?' Instead, we would ask 'Do you want to buy this computer?

You normally use the auxiliary "do" for the following situations:

Asking Questions
Making Statements: (Negative, but not positive unless you need to emphasize on something) e.g.
a) No, I don't like ice-cream.
b) Yes, I DO like Mary. (Emphasis)

If it is a statement:
1. in simple present tense
i). About a habit, e.g.
a) Do you go to school every day?
b) Do they eat American fast food?
ii). About facts, e.g.:
a) sun rises,
b) water falls...
2. non-third-person singular (NOT HE / SHE / IT)

If you ask:

"Do you buy computers?" = 你(習慣)買電腦嗎?
"Do you buy this computer?" = 你(習慣)買這部電腦嗎?

Is that strange if you ask something similar even in Cantonese?

1st sentence
係現在/果一刻你會唔會買

2nd sentence
係以後/將來你會唔會買

Do you buy this computer?
it means you are not buying computer at that time...
you are just shopping...

Will you buy this computer??
this sentence mean you are buying computer at that time...you have to decide what kind of computer you need to buy ...