Viewsonic g90f+

hi i trying to play 1080 movie around 4 and 6gb size.
the issue is that when i play it it skip few seconds of screen now and than. while the audio is running accordingly.

this is all my spec below, now i need to know should i change my display or the motherboard or etc.

amd athlon 3400+
430 watt cooler master
1 gb ram (512*2) DDR
Msi motherboard 7228 built in video card and sound card+lan
viewsonic g90f+ CRT monitor
HDD 250gb
dvd rom

now i know it is old and it is working fine on XP so i am not that interested to change everthing. so if i change my monitor to LED monitor 20inch or 23inch or even 24inch
which one is best to buy and second would changing the led monitor fix this issue or not. if not what will. so i plan to buy first accordingly.

oh while 720p is fine when i last played on it 3gb file