I use xampp for local development in elgg and I haven't had any of those issues - nothing special either - default config.  Is it the case for a clean elgg installation or do you have a bunch of plugins installed?  It's possible that a poorly programmed plugin could be getting caught in a loop or using an external resource (via curl perhaps) that is hanging and timing out silently.

Check you error logs - C:\xampp\apache\logs\errors.log

I've found that anti-virus software can really hog CPU cycles when running Elgg locally.

After deactivating all of my plugins and activating them one by one it seems that part of the problem (if it is one) comes from plugins calling elgg_load_js. This routine seems to be quite resources consuming. there are several ways of loading js in a page using elgg (elgg_load_js, elgg_extend_view, link) What is the better practice? Also should elgg_register_simplecache_view be used for every js and css views?