Check for the crawl errors manually which appears in Google Webmaster Tools, and if you are able to open your URL, then you can re-submit your sitemap.xml file to GWT, and within few days, it may get fixed.
If you find any broken links, remove it from sitemap.xml file, and the submit your sitemap file to GWT.
Make proper 301 re-direction wherever applicable, fix all the errors, it will make your Website trustworthy