Domain and all subdomains disappears.

[TomH27]

hi folks!

i have a subdomain with several hundred incoming links from clean sites. no linknetwork or something in this direction.
there was no black-hat methods ever on this domain. last wekk the main-domain disappears from google within my subdomain.
my subdomain was into the top-ten with my main keywords for about two years.
the subdomain and the maindomain have still a pr of 6.
what can i do? what could this be?
an ideas?

regards, tom

[tedster]

How many subdomains total, and how many urls are actually there for each subdomain, in addition to the index page?

[TomH27]

just one subdomain.
the subdomain icludes 3 pages.
the main domain includes 20 - 30 pages.
there were no changes in the last few months.
i sent an email to google but get no response what the problem could be.