问题：
昨天一步小心拔了插座，早上过来idea就打开不了项目了，查看日志文件C:\Users\Administrator\.IntelliJIdea2017.3\system\log ，发现抛错如下：

Caused by: org.xml.sax.SAXParseException; lineNumber: 1; columnNumber: 1; Content is not allowed in prolog.

	at org.apache.xerces.util.ErrorHandlerWrapper.createSAXParseException(Unknown Source)

	at org.apache.xerces.util.ErrorHandlerWrapper.fatalError(Unknown Source)

	at org.apache.xerces.impl.XMLErrorReporter.reportError(Unknown Source)

	at org.apache.xerces.impl.XMLErrorReporter.reportError(Unknown Source)

	at org.apache.xerces.impl.XMLErrorReporter.reportError(Unknown Source)

	at org.apache.xerces.impl.XMLScanner.reportFatalError(Unknown Source)

	at org.apache.xerces.impl.XMLDocumentScannerImpl$PrologDispatcher.dispatch(Unknown Source)

	at org.apache.xerces.impl.XMLDocumentFragmentScannerImpl.scanDocument(Unknown Source)

	at org.apache.xerces.parsers.XML11Configuration.parse(Unknown Source)

	at org.apache.xerces.parsers.XML11Configuration.parse(Unknown Source)

	at org.apache.xerces.parsers.XMLParser.parse(Unknown Source)

	at org.apache.xerces.parsers.AbstractSAXParser.parse(Unknown Source)

	at org.apache.xerces.jaxp.SAXParserImpl$JAXPSAXParser.parse(Unknown Source)

	at org.jdom.input.SAXBuilder.build(SAXBuilder.java:518)

	... 123 more

解决办法：
去C:\Users\Administrator\.IntelliJIdea2017.3\system\caches目录下，将缓存文件夹下的所有文件都删除掉，然后就解决了。值得一说的是，这个方法能解决大多数因idea原因导致导入项目失败的问题。