Hello, Tenma ?
0, check your setting in Sony Vegas... try experimenting different export format just to check if it is the software issues.
1st, Check your pc component health... memory module, motherboard, CPU, GPU and others. The easier way is by running a software to test hardware health status.
2nd, make sure you have enough storage space left for your video project.
3rd, update your Sony Vegas software, and PC OS and each hardware components.
4th, Disable GPU rendering, only using CPU... or vice versa.
5th... let's talk again about many other stuffs.
Hmm, it also could be a overheating issues, since said it will crash after a while. But... it could be the content you r rendering too, such as effect or something else which are buggy.