I have ordinary Pakistani passport with valid USA visa. Can I be granted Turkish tourist visa for seven days on arrival at Istanbul airport?
Official passport holders are exempted from visa for their travels to Turkey up to 90 days. Ordinary passport holders are required to have visa to enter Turkey. Ordinary passport holders with a valid Schengen, USA, UK, Ireland visa or residence permit may get their one month single entry e-Visas via the website www.evisa.gov.tr.
Since you have a valid USA visa, you can apply for an e-visa from the link given above.
It seems yes, if you have an hotel booking and adequate financial means. (source: https://en.wikipedia.org/wiki/Visa_policy_of_Turkey). But this is just Wikipedia.
You may need to look on Turkey embassy website of Pakistan for better information.