English is not my first language, so I apologize in advance if something isn't fully understandable :)
To the point: usually a crash on startup is caused by a bad load order. The order in which the mods load is important for Skyrim. It can also be caused by mods requiring Dawnguard, Breezehome or other official DLCs.
If you're using the Nexus Mod Manager (and I recommend everyone to use it, it's wonderful __^ You can download it here: http://www.nexusmods.com/skyrim/mods/modmanager/?) the easiest thing to do is to check the "Plugins" tab, verifying every esm or esp dependency (when you select a plugin in the left column ou get its dependencies info on the right). If something requires you to have Dawnguard but you don't have it installed, that's probably the culprit.
If this does not solve it you can try BOSS to sort out your load order.
Here you can find a guide to follow in the troubleshooting process, but it's quite automatic... it will re-order your mods according to a safe "master list", that is, a load order checked for consistency that should give no problems.
If it crashes again after the re-ordering, you might want to try TESedit.
On that page there are full guides for everything it can do (it's quite a powerful piece of software), but basically you only need to install it, fire it up and let it run with default settings, without selecting the master files (Skyrim.esm, for example). If something's wrong it will stop analyzing your mods. Check the last mod it was working on when it stopped and you'll have the mod (or one of the mods) that's causing the crashes.
Rinse and repeat until everything checks out.
Hope it's helpful... I don't have time right now to add further details but I'm sure you'll manage with a little reading and video tutorials. This is just to put you on the right tracks ;)