Plug it into iTunes. Hold menu and select button. It should restart twice. Don't let go of the buttons. iTunes should then say iPod is In recovery mode allowing you to restore it. If it doesn't check if it sounds like the hard drive is failing
Can you be more specific in what is taking ages to load? You can run a basic apple hardware test on your mac (boot mac holding D) this would verify the major hardware components are fine, in my opinion it sounds either software based or hard drive related but i wouldn't confirm this without more information. If its taking ages to boot up and load the home screen; do you have lots of items on your desktop? Or do you have loads of startup items. (system preferences - accounts - your user - login items and delete everything in there then try a reboot.
If it's liquid damage and you wasn't grounded when you repaired it you've probably made it worse. Your best bet is to check connections 1&2 for the screen and make sure cable 4 is nicely seated. Under the screen by the home button there is two pins that stick out. This is how the home button makes contact with the board, make sure these are not damaged.
more than likely you have just damaged the top case of the mbp. If its a 2010 then you need a whole new top case as this contains the keyboard as well. They have a black shield underneath the keyboard so hopefully. To be honest your under warranty, although Apple void a warranty if liquid damaged just be honest with them and they may cover it for you
If its a stop sign then its an error with the hard drive, the mac cannot boot from the boot.efi files iirc. Ideally you would want to use disk utility to verify the disk first. Take it to an Apple store they would be happy to check if it is a hard drive and whether it just need an erase and install or a complete new hard drive. Boot the mac in verbose mode, hold cmd v on boot and paste up the bit where it fails