Replaced Hard Drive stopping applications

I???ve got an old Canon laptop computer pre 2003. It had been running very slowly and then I got the full blue screen. The hard drive has been replaced with a generic hard drive by a computer repairer, however after about 3 weeks my laptop is able to boot up but my applications are failing to load. I have reloaded the applications and this hasn???t helped. Could this still be a hard drive issue?