The home page of my website has been indexed by Google more than 6 months ago. Some of the internal pages have received a page rank 6 or higher, however, the page rank of the home page remains 0. What might be the reason and is there anything I can do about it? Thanks!
A page is assigned PageRank as soon as it is indexed as all pages start off with a default PR (which I think is .15). However, that doesn't mean you'll see that PR in a toolbar or reporting tool. Public PR is updated only periodically so whatever PR you see via reporting tools is a snapshot of the past. It does not reflect a page's current PR.
Keep in mind that toolbars and other reporting tools can be flawed and not reflect a page's proper PR. It's also possible that the home page has received a penalty for selling links or something similar. Do you sell links or advertising on your home page?
How does your home page rank in the SERPs? If it is doing well I wouldn't put too much energy into figuring this out. If it ranks poorly then there is an issue somewhere that needs to be addressed and you should find out what is causing your home page to behave mysteriously in the SERPs and with its PR.
The PR cycle is a bit mysterious, but it's been suggested that PR changes are usually visible somewhere in the midst of a 90 day cycle.
The fact that your sub pages have page rank means that the PR of zero on the home page is quite likely accurate (i.e. it's not an issue of waiting for Google). If that is indeed the case you need to look at why your subpages have high page rank. Are there a lot of external links coming in to these pages? Is there a specific keyword string you've been ranking well for on those pages? Compare all the pros and the cons between the pages on your domain that are ranking well and those that aren't and you'll hopefully get some insight.