Its sounds like you have a double hung window that slides up and down check to see if the outer top window can slide up then lock it. If the glass is sperating from the frame you can take it to a glass replacement company and they will fix the frame and glass if not vinyl welded

I would recommend replacing the window.

sealing or adding any aftermarket seals would most likely sacrifice operation 

The glass package and the insulation of the window are the most important. The best window would be quadriple or triple pane window with foamfilled sashes and krypton or argon gas inbetween the glass. The dense gas keeps the cold air out in the winter and the hot air out in the summer. The foam filled sashes keep the insulation like your walls. Also choose vinyl over wood for better insulation, 

the most important thing you need to make sure you have is a highly rated low-e window. low -e will reflect the solar rays away from the inside of your home so it doesn't heat up during the summer or direct sun etc and during the winter it works in the opposite manor. winter it will keep the heat inside your home keeping your house comfortable. there are many good brands of windows like Andersen, Western, Hurd, Marvin, Eagle (andersen), just to make a few. be sure and do plenty of research and get estimates from. 4-5 companies and compare dont just get estimates from 1 or 2 companies. good luck. 

Check the weepholes and make sure they are not clogged. These holes allow water to drain outside of the window, and are on both sides of the window. If they are clogged then the water will drain wherever it can - inside your walls and house. When the window is closed, you are making it harder for the water to get inside. I suggest taking the tip of a knife and just cleaning them out to see if that helps. 

Is there a leak when it's raining or is it just when the window is open in general? If it's simply when the window is open, then there could be several varying possible reasons as to why the basement leaks, solely when the window remains open. Bad timing, as off putting as that sounds. If it's when the window is open during a rain fall, the window could have lost its seal. Rain could leak in through the wall and then to the basement ceiling. If that's the case, I would recommend a new window seal, or replacing the entire window altogether. If you have further questions or concerns, please feel free to call our office. 403-343-0393. Thank you!

Hey Geoffrey! To leave a review for a GuildQuality member, simply search for the company on our Find a Contractor page, and then click on their profile. In the upper right-hand corner, you will see a button that either says "Add Feedback" or "Leave Review". Once we receive your feedback, we'll mail you a postcard with instructions on how to verify and publish your review. We rely on this verification process to ensure that all feedback published is from actual customers. Let us know if you have any other questions!

If you go to the contractor's guildquality profile, or search for the contractor on guildquality's home page. See Attachment, and then once you go to their profile you can select the blue button that says Add Feedback, you can then select write a review or complete survey if you have a code for the survey. Hope this helps.

Guild quality will reach out to you for a small survey or you could go to the Mid South BBB to leave a review