Mike, not sure how you have tried to remove it.
Try this, if it is runninng do a ctr,alt,del to get to the close program function. Close everything that you think should not be running. You will have to do this repeatedly for each item you want to close.
Afterwards try removing them through the control panels remove function.
If that does not work you can do a search for items installed in the most recent days. Then delete the actual folder from windows explorer. This is not the best, but it can be done. You might have conflicts and errors, but may not.
Last choice is to do a complete restore. CAUTION, restore will erase EVERYTHING you have done. If there is anything you want to keep, favorites, pictures, etc, go in and put them one a disk or something. One thing I have had people do that could not put large files or did not have a way of storing things seperatly was to email the items to yourself, but do not reopen email until after the restore.
Each computer is different. I know you just got this computer so please read you manual for info.
Last but not least there are a couple ways to lock you computer, one is to break your roomates fingers!!
Second is to do a seperate login, but that still allows him access.
Third is to get into you bios upon start up and activate a master password. I have this on the laptop but never done it on a desktop.
Each computer is different to get into the bios, but most commom is F2, F8, or F10 key to press when it first boots. There is usually a cursor flashing just prior to fully booting. Read you manual to find out how yours operates. There should be a menu to turn on a password. Word of CAUTION, do NOT forget this password. The ONLY way to clear is it by doing a complete factory restore. You will LOOSE everything when doing a restore.
Now, I am no computer expert, but these are things that I have done and it works.