Windows 7 BSOD happens randomly here and there.

Hi,
out of the 4 dump files posted, 3 were like the above and one is a Bugcheck 1E. The causes for Bugcheck A can be:

This bug check is issued if paged memory (or invalid memory) is accessed when the IRQL is too high.
The error that generates this bug check usually occurs after the installation of a faulty device driver, system service, or BIOS.
If you encounter bug check 0xA while upgrading to a later version of Windows, this error might be caused by a device driver, a system service, a virus scanner, or a backup tool that is incompatible with the new version.

Click to expand...

https://msdn.microsoft.com/en-us/library/windows/hardware/ff560129(v=vs.85).aspx
Bugcheck 1E is usually caused by:

This is a very common bug check. To interpret it, you must identify which exception was generated.
Common exception codes include:

• 0x80000002: STATUS_DATATYPE_MISALIGNMENT
  An unaligned data reference was encountered.
  
  
• 0x80000003: STATUS_BREAKPOINT
  A breakpoint or ASSERT was encountered when no kernel debugger was attached to the system.
  
  
• 0xC0000005: STATUS_ACCESS_VIOLATION
  A memory access violation occurred. (Parameter 4 of the bug check is the address that the driver attempted to access.)

Click to expand...

https://msdn.microsoft.com/en-us/library/windows/hardware/ff557408(v=vs.85).aspx

Unfortunately the dump file containing Bugcheck 1E was corrupted and so I couldn't get the exception code (the reason behind the crash).

In conclusion the dump files do not mention a specific driver although that doesn't always mean one isn't involved somewhere along the line. It is possible that your issue stems from either a driver or Bios issue, a system service with Windows which has become corrupted or a hardware failure typically RAM. Oh I also forgot to mention that with bugcheck A the anti-virus app can also be a primary cause.
Usually I can glean from the dump files which machine your using but unfortunately all I can tell is that it's a Lenovo presumably a laptop? I checked your drivers and they are in need of updating if possible. I say if possible because laptop drivers are supplied by the manufacturer and they are not always up to date. If you know the where to go to find the driver page for your machine I would check what updates are available. If not then post the make and model and I'll point you in the right direction.

If you recently added anything new either software or hardware (this includes windows updates) then did it coincide with the start of the bsod issue? If so try removing said update.

Check for corruption within Windows by running the system file checker. Find command prompt, right click on it and run as admin. Type:
sfc /scannow
Press enter and await results.

Windows does have it's own memory testing app but it can often miss errors and the best app for the job is Memtest86. The latest version of which can be found here:
http://www.memtest.org/

To run Memtest86 you need to either burn a copy of it to disk or use a USB stick. If you look down the page you'll eventually find the latest version and it's associated downloads. If your burning to disk choose the pre-compiled iso zip. If your using a USB method then the corresponding download is the auto installer for a USB stick.
Once you have Memtest86 on the media you selected you'll then need to enter your bios and change the boot order so that the machine will boot from either the disk or stick you have Memtest86 on.
Run the test for at least 12hrs if possible unless it becomes clear that there is a issue. If there is a problem with the RAM you'll see the errors pop up in red so you can't miss them.

Post any new dump files.