Well you're having crashes. The best thing to do would to be back up all your data and documents and do a system restore with a new OS install. Can't give you further instructions on that because I don't know you're computer model. Let us know.
Check your temperature. Maybe your CPU is overheating. Check if the CPU fan is spinning. If fan is still spinning, it may be that the contact between the CPU and the CPU cooler got loose in which case you need to reseat your cooler. Make sure you apply new thermal paste. You can download and install everest to monitor your temp.
It is cpu lag and often a bottle necking with in the system ram. There isn't much one can do besides ram and cpu upgrades. As for data don't back it up on the same drive its pointless if you had a failure. Even burnable CDs and DVDs wouldn't be that bad of a backup option for important stuff like tax returns, pics, work exct.