Unity is crashing alot!

Today i did a registry clean up on my computer and deleted a lot of unneeded programs,i restarted my computer and went into unity(my every day place!) to start on a new terrain for my game.Its a large terrain the resolution is 4,000x4,000 and hight of 700.Im a pretty fast worked and noticed when i get a little click happy and try working a little fast unity starts crashing and since unity doesn’t have an auto-backup feature it is a very bad thing when it crashes.It has crashed around 3-4 times in the past few hours.Could this be from me cleaning up my registry?

Do you suggest i re-install unity?

Do you think the terrain is just so large my computer+unity is having troubles handling it?

My specs
Vista 32-bit
AMD Athlon 64 x2 Dual Core Processor 5000+ 2.61 ghz
4.00 Gb Ram
And 500 GB Hard Drive
nvidia gforce 8500 gt video card.

I also got a fatal error message that unity was out of memory in the process of it crashing out!

I restored my computer back 1 day and the things i was doing before that would cause unity to crash seem to be working ok.Any suggestions are still welcomed!

As far as it the auto-backup feature concerns I would like to recommend our Auto Project Backup, which you can find in the asset store.

I have issues with Unity locking up a lot, but it usually when I am trying a “Build Run” to my Android phone.