What's the best way to take a desktop on a plane trip?

I'm going on a trip to Los Angeles an will be using Spirit Airlines. However, I'm planning on taking my HP ENVY 23-Inch All-in-One Touchscreen Desktop with Beats Audio and was wondering what was the best way to take it with me?

Best way to travel Europe?

Next year, on July 5th, I will be backpacking Europe for 3 months starting in Copenhagen and traveling to about 20 countries/stops. I'm still trying to figure out the best way to travel around. I have a general idea on where I'm going but it's not a set schedule, so I won't be able to buy months in advance flights. If I go with budget flights I would be purchasing the ticket in less than a weeks advance. Would it be smart to buy a 3 month Eurail pass or just stick with budget airlines? Are there any other means of transportation that are easier/cheaper? Also any other tips for backpacking for an 18 y/o male would be greatly appreciated.

Can i be rebooked with a different flight?

I had a little bit of a crazy morning and ended up missing my flight home. They told my that I can be on stand by on the next flight or pay $200 for a guaranteed spot. Unfortunately, they only have one flight to Honolulu daily, which means I will be missing Christmas morning with my family. I'm wondering if I should have asked the agent if it's possible to be on stand by with another airlines that have flights today (Christmas eve day) so I can be home by tomorrow?