From the Force.com IDE FAQ:
Where can I find extra information, such as logs, to troubleshoot a Force.com IDE issue?
Force.com IDE logs are stored here:
$workspace/.metadata/.plugins/com.salesforce.toolkit/force-toolkit.log.
You may view these logs at runtime using Eclipse's Plug-in Development
Environment's Error Log view. Log level is set in the Force.com IDE's
/log4j/log4j.xml configuration file.
Where can I find extra information, such as logs, to troubleshoot a Force.com IDE issue?
See the page on developer.force.com