Alright so, I'll include a tl;dr at the end but I figure the more info the better I can be helped.
A week before Christmas I received all the parts for a computer I was going to build (first time). I put it together with a friend who has built two before. Everything went smoothly and I borrowed a monitor from another comp to install Vista. I wasn't going to get a monitor until Christmas so it sat there for a few days until then. The day I got the monitor I attempted to power up my computer but nothing would happen. No fans or anything. The only thing on were the LED's on the mobo and the LED next to the power button (which made me think it was in sleep mode or something). I tried several things, and after reading about it I reseated the RAM etc. I had pretty much given up and assumed there was some faulty hardware. I leave the room and come back and my computer is running.
All goes well for a week or so until one day I power it up and walk out. When I return, the comp is powered down. So I have no idea if it shut down or just turned off. I can't remember but I believe it powered back on normally.
Then I must return to school. I take my desktop to school (2 hr drive) and get everything plugged in. When I try to boot it, nothing turns on again (just some LED's, no fans). My friend was over and said maybe i need to leave it plugged in the outlet for a bit so it can get power. So I wait a few mins and press the power button. It works.
This time I go 2-3 weeks with no problems. This morning I wake up and it won't turn on. Same issue, the LEDs work and all. I try unplugging things, letting things sit for several mins and nothing is working. I didnt try reseating anything since it hasnt moved in weeks. I'm gone most of the day and come back and try to power it some more. No luck. My friend comes over and were in my room. I dont even touch it, but my computer turns on. All the fans and everything.
So, I'm left with a couple options. From what I've been reading it is most likely the PSU (and I hope, bc a new mobo would suck to install). I can buy a PSU tester for like $15, get a full diagnostic from a comp shop for $50 (or just PSU tested for $25 but its cheaper to buy one off newegg!), and of course the PSU and I believe mobo both have warranties. 2-3 years I think. So whatever hardware it is should have warranty.
What should I do? What sucks the most about an exchange is that I have to wait. Even though my computer is working now, I feel at any point it could shut down and stop working again. But I'll deal with it. What is my best option? Does it sound like PSU? This is my first time building a comp, and obviously troubleshooting one. So my knowledge is very limited.
Here is a list of the parts I ordered in case it helps:
# 1 x APEVIA X-PLEASURE-BK Black Aluminum ATX Full Tower Computer Case - Retail
# 1 x EVGA 123-YW-E175-A1 LGA 775 NVIDIA nForce 750i SLI ATX Intel Motherboard - Retail
# 1 x EVGA 896-P3-1267-AR GeForce GTX 260 Core 216 Superclocked Edition 896MB 448-bit GDDR3 PCI Express 2.0 x16 HDCP Ready SLI Supported Video Card - Retail
# 1 x SILVERSTONE OP850 850W ATX 12V 2.2 & EPS12V SLI Ready CrossFire Ready Active PFC Power Supply - Retail
# 1 x Intel Core 2 Quad Q9550 Yorkfield 2.83GHz LGA 775 95W Quad-Core Processor Model BX80569Q9550 - Retail
# 1 x OCZ Platinum 4GB (2 x 2GB) 240-Pin DDR2 SDRAM DDR2 1066 (PC2 8500) Dual Channel Kit Desktop Memory Model OCZ2P10664GK - Retail
# 1 x Microsoft Windows Vista Home Premium SP1 64-bit for System Builders - OEM
# 1 x Western Digital Caviar Black WD6401AALS 640GB 7200 RPM SATA 3.0Gb/s Hard Drive - OEM
# 1 x LITE-ON Combo Black SATA Model DH-52C2S-04 - OEM
Few days after building comp, wont boot up(only LEDs on mobo and near power button). Boots randomly while im away. Later randomly turns off while I was away. Then takes a couple tries to boot after a 2 hr trip in the car. Then today turns off and wont boot until randomly turning back on at night. PSU? Mobo? First comp I've built so my knowledge is limited.
Thanks for your time and input.