Here are some common issues with HCL and the ways to fix them:

White Screen of Death (Usually at install):
This is caused by garbage characters in the config.php or version.php (both slated for removal in version 3.0.0).  See this topic for more info on the fix

Erratic behavior, it looks like everything should work, but doesn't:
Very likely your host has short_open_tag off, this MUST be on in all versions 2.1.3 or earlier.  See this topic for more info on this issue.

Microsoft IE 6 & 7 issues:
Please ensure that you have a current JAVA plugin and that you have set your server as a trusted site.  This has solved many issues with IE.  Always try another browser (i.e. FireFox or Opera), if they work, double check IE.