Sidebar Relocated to Bottom

Hello,

Just inserted the code for an advertisement to my sidebar, after I added it I saved it and noticed my entire sidebar had moved from where it should be on the right hand side of the page (I’m using Arclite) to the bottom of my home page and is now centred under my first entry. I quickly then removed the ad coding and tried to resave it again but the sidebar still appears at the bottom center of my home page. I haven’t a clue what I did wrong. Any idea how I can easily correct the problem?

With much thanks and appreciation for your time,

Sherrie Ellen