A new website indexing problem

The number of pages indexed's been decreasing

[Moby_Dim]

The situation is: a new site of about 170 pages started 1.5 ago. No G.submissions, just a link from theme related page (pr5). All pages (or the majority) were spidered, and about 75 of them were indexed (allinurl:...).

Then there was a 8-10 days period when robots.txt denied all spiders, then opened again. No changes in pages were made. The index page PR appeared (=4), all other pages are pr0. But at the same time the last week main problem - the number of pages in G.index (allinurl:w*w.sitename.c*m) is permanently decreasing (75 -> 56 -> 45...). Now the number is 12! but the index page pr is still 4. And G/bot does not want to return :(

Can anybody explain this? Thanx.