If you got GRUB messages then you got a Linux bootloader on your boot HDD and likely is the (a) problem.
How it got there either something you did or something malevolent.
Either way the cure is to wipe the zero sector and repair it. Not for the faint of heart. Backup the drive image first, then pull the 2nd drive temporarily. Reinstalling Win7 won't cut it...you must destroy all partitions and reform them or nuke zero sector which Seatools (DOS) will do. Wouldn't be much of a boot loader if loading an OS touched it now would it.
As for testing PCU and MB an excellent request. Unfortunately nobody really has any testing apps for them. That is really inexcusable IMHO for the CPU and GPU makers.
As for test apps:
memtest86 (not memtest86+) is the only 64bit app around for testing RAM.
Seatools for DOS is a good HDD testing app.
Windows own Device Manager, MSINFO32 (see components>problem devices) and dxdiag are useful testing apps...there are some others for network testing, process monitoring, etc....
Try an External build, tear it down to a minimal functioning system, lay the main board (helps if speaker connected to front header or embedded on MB for beep codes; or if any diagnostic LEDs, LCD are present) on a piece of plain brown cardboard or other non-conducting surface with only a Keyboard, one stick of RAM, CPU, HSF, PSU and monitor to rule out shorts as well as bad components. [Temporarily use onboard graphics if available otherwise use your video card.] Switch RAM stick and slot location. Add one component back at a time. This will rule out components and maybe rule in the defective part. If you have any known working parts that can temporarily substitute this is a good time to try them one at a time.
MSI Kombuster = GPU
Heaven = GPU (DirX11)
Prime95 = CPU
LinX = CPU
Memtest86 = RAM
OCCT = CPU + GPU (PSU load test)
AvP Benchmark (GPU, DirX11)
Furmark = GPU (OpenGL)
Tessmark = GPU (OpenGL)
Just be careful with the OCCT one as it will kill a cheap PSU pretty quick and ... [maybe] the rest of [the] PC when it goes. You are better off just researching the make/model of the PSU than actually testing it.
In addition to 7byte (who also have a burnin app) mentioned by another responder,http://www.passmark.com/products/bit.htm
BTW, I am not suggesting you use any of the above except Seatools. Waste of time IMHO. Just answering your question.
You can pretty much load whatever you want onto UBCDWin following their directions up to the 9.5Gb limitation of a DL DVD+R.
I strongly suspect it is not a hardware issue but a bootloader issue. Free beyond a bit of time. Quite provable by booting up an Ubuntu LiveCD and playing around. Bet there are no problems which means either a HDD [Seatools helps rule that out; actually Ubuntu's Disk Manager has a nice tester too.] or OS problem (in this case bootloader).
Please list all your hardware for more specific help. [List specific make and model number for every component in system and attached to system and don't forget the case. If this PC is from a major PC builder, list the make, full model and complete model number too. List BIOS version too. Don't forget any parts you upgraded or are trying to install. Links are greatly appreciated as they remove part ambiguity and why should we have to look them up? Be sure to include the full OS version and bit and service pack installed.]