Windows 7 isn't a bad os but what might be the problem is maybe your computer is too weak/slow. In order to run it good I'd recommend these specs A dual core cpu @2.0GHz or higher 3GB ram or higher a 5400RPM HDD or higher a GPU with at least 128MB or higher
another thing is whether you hdd is nearly full, if your hdd is almost full it might lag a little. Check if you have the latest drivers installed. Just to give you a little info, drivers are pieces of data that are the newest versions of code running pc parts. What it does it people update the code so your pc parts will be more stable, so if I were you I'd check that out. If you want to really speed your PC and you know how to install a Hard drive inside your pc, you could back up your OS on a Solid State Drive. They are a bit pricy starting at $50 but it might be worth it. Maybe you don't even have to do this stuff, maybe what you might have done is you didn't give your PC a clean install. If you upgraded from XP or Vista, this might be the case, if you clicked upgrade what could happen is it can make your system glitch up since the 2 OS don't cooperate. So what you might do is save all your important files and then reinstall a clean install. This might be the only prob, what ever the problem is, the vast internet is there help.
if you can start it in safe mode do a system restore , if not , ive started a pc thats courrupt and while its running jerk the power cord out of the power supply wait 3 mins plug it back in and windows it self should start to look for that last known good windows setup and then start it , follow any promps after that remember to defrag and after this id check system restore and go back as far as you can then go to the hp site and get all the updates from that point foward . have a great day