Write a letter of readmission to my college

I started college right after high school. I wasn't the brightest in high school, but I vowed to try my hardest in college and, believe me or not, I did. I studied, hired tutors, stayed after class to ask questions, and still I'm as dumb as a donkey. I got academic probation the first year and they told me a have a semester to improve my grades and get academic probation revoked. So, I tried to get my grades up and I did! But it wasn't enough to take me off of academic probation. So I got suspension or whatever. So in my sadness and stupidness I took 2 years off. And all that time I was so mad at myself that I didn't bother to find a way back in. Till now. I found out if I take a year off, I can reapply and start a clean slate. Well I took 2. I want to go back to college but how do I start. I want to write a letter to the school and tell them about my problem and ask for help but I don't know how.
Please help! Thanks.