MacBook won't turn on... Get to apple logo then just a white screen. Last night I could attach files to a website while applying for a job nor could I attach it to an email in safari and my computer wouldn't allow me to open my mail. HELP!!

I upgraded to iOS lion and ever since my computer takes about 5 mins to turn on and is just so slow in everything. It is probably the worst decision I made to upgrade to it. But ever since getting an ipad I rarely use it. Only to back up my ipad and my iPhone.ive never really had any issues with it untill now. Last night I was trying to apply for a job so I was trying to upload my resume to a website and everime I would upload it it would crash. And I couldn't open my mail nor could I attach this file to my email in safari. I'm stuck.. Please help. My computer is about 3 years old but I though these products were meant to last forever...