Potential PSU problem

[neallseamus]

Just put the finishing touches on my new PC, and having a vague boot problem. Upon turning the computer on, all the lights and fans start working and the monitor goes to the ASRock boot screen, then it shuts down. Sometimes it doesn't turn back on unless I disconnect the PSU, other times it starts and shuts down repeatedly. At one point, it started up correctly and I installed the OS successfully. About 20 minutes later, same thing starts happening again.

Now this is a common problem that can be caused by many things, I know. So far I do believe it is caused by my PSU being too weak.

Specs are as follows:
ASRock b75 pro3-m mobo
intel i3-2100 3.1ghz cpu
asus geforce gt640 2gb gpu
2x corsair vengeance 4gb 1600 ddr3
apevia x-qpack micro atx case

My PSU just came with the case, it's a 420W.

So, my question is; is a 420W power supply too weak for the specs I have? And is it a safe assumption that that is what is causing by boot issue?

 

[jerry6]

Apevia 420 watt psu , probably the problem

 

[neallseamus]

Now I've been looking everywhere, and matx psu's don't come much more than 420W. Anything I can do to solve this power problem, or do i need a new case/mobo/psu?

 

[obsidian86]

it takes a standard atx psu where you buying from and whats your budget?