UE4 freezing

Hello, I have problem with UE4. I made simple levels (nothing big). First week i had no problem, I opened level with no problem but now i open level and whole PC just freez. Not just UE4 but other applications as well. I dont think the problem is PC because i have gaming PC witch suppost to run best games with no problem. When it freez the only option is reset whole computer. I dont want delete level because i work on it pretty hard. If it happend to you as well can you give me some good advice how to fix it? Thanks.

Try to wait bit longer it might need some more time.
Once i had to wait almost one hour.

But first time it launch like in 10 seconds and now i wait 5 min and nothing… I try wait more but i dont think its gonna launch. But thanks for advice.

What loading percentage is it stuck at?

Hi when i click on it. It looks like its gonna load but it stuck at 20% (but this number is changing) and than i have to reset PC because there is no other way. I try wait for 5-15 min. but no progress.