Hello,I have this desktop and is working fine , I installed a windows 7 ultimate for a while and is good the only problem I have is a grafic card but I already upgrade it , now I am looking to replace a original harddrive 250 gig for a 750 ...but this pc have just 1 slot , doesn't have a open space s to install an aditional one ...since this is a C drive I need some instructions help to how I can do it ? ....also it is true to I can put any harddrive size in this pc ? ...I was thinking to put a 1TB if is ok , please let me know and thanks