Bad Sector?

Before spending time for complete re installation, It can be good idea to check that everything except HDD is ok:

1. Check that the problem is really HDD (not HDD controller, for example):
   • download http://www.hdtune.com/files/hdtune_255.exe (free for personal use). Do test, check the Health tab for some "SMART" error. You can also try Error Scan. If you see (at least one of ) errors, SMART health is not ok, there are parts with good speed and parts with bad, the problem is HDD for sure. If everything is good (but transfer speed is constantly low), I recommend recheck it with other computer
   • download some Linux live (for example http://www.ubuntu.com/download/desktop ), and start is in "Try" mode (without installing). If it does not work at all with your laptop, it is simply not compatible. But in case it boots, but you get some (not graphic related) problems (slow, hang, "kernel panic", etc), there is something wrong with the rest of your computer. Check RAM (an option during Linux boot, as I remember modern Windows also have one). Check the temperature (of CPU, HDD and Graphic).
2. You can make safety copy of your whole HDD, in case it is still readable (can take a while in case it is half broken...). Free tools are a bit harder to use, but they do the job. For example http://clonezilla.org/ . You can save the image on some network storage in case you do not have spare disk. In case you clone to real HDD, you can try to start/reinstall from it. That not always works, but you can find relevant info in the internet (once you see the error to solve). 

If you have the utility program from the manufacturer, then you should have made some DVD (about 3 for mine) from the program to install Windows 7 on a new harddrive.
 
If only part of your harddisk is bad (and not the complete C:\ partition which contains the master boot record and OS) then you only need to right click on the Computer desktop icon and Open. Right click on the C:\drive and select Properties. There you will see Tools, and select both look for bad sectors and check the disk (which checks the OS).
You have to restart the computer to do that, and there are 5 sections to all of that, and depending on how big your partition is (checking the harddisk for bad sectors so Windows can mark those not to use) then if anything is found wrong Windows 7 should be restored, you will have your harddisk checked so it does not happen in the future unless the harddrive fails completely and then after Windows is started, look for a program that creates the DVD from the manufacturer that is Windows 7 - because they do not supply that anymore with the computer. It should contain everything you need because the computer does not hold the registration number like with XP on the computer maybe and there is no sticker on your computer perhaps with that info but it should be included with the manufacturer's programs to restore your computer. In the past you put the DVD in like with XP and re-installed Windows XP and went through all of that.
 
Now you have to make your own DVDs (it took three on mine) and store them somewhere along with a Recovery DVD and anything else included to make the OS work again.