First of all, how old is your site? Second, do you have any external and inbound links. Third, does it have any content?
Appearing on Google for new sites can take some time.
Also, the more links - the more weight it will have in SERPs.
You need content - the more the better.
It would be much better if you provide us with more details, such as: which exactly SEO methods you have used, give us a link to your site, probably you need some on-page improvements, did you updated you content since you create a website, ect. After this we might be able to help you somehow, but now - we cant, sorry.
Generally speaking, PR would not be a decisive factor for SERP. If you want to keep your ranking high, you need to optimize your title tags, meta description tags, h1 tags and page contents using your targeted keywords plus keeping building enough backlinks using your main keywords and their variants as anchor text.
PR is not have much role for serp's If you have low but you are doing good seo and quality work for your site then definitely your site serp's will be increase. You should try to get back links from high PR do follow sites and related to your niche. You should analysis your keyword and content again.
Ok... Here is my take. I know a lot of people have said an array of different things but I have to agree on this one with Fred. Do not worry so much about PR, that is something that happens every three months (the update at least). Whereas your SERPS can get affected everyday by the SEO work others are doing to their respective sites. Do not continue searching for details on your keywords and so on. Or whatever it is that you are doing. You need to continue your SEO efforts. Most people seem to overlook the fact that SEO is an ongoing process. Competition is fierce and there are MANY people competing for that #1 Spot. SO GET WORKING!!!